i've recently decided to be a 7-string player primarily.
i got a 7 string around 2005 when i was gigging regularly with a 5 piece band. my bassist used a 5-string and i thought it would be cool to do some unisons on the low B string. but at the time, i just wasn't ready musically to add that 7th string. most of what i played on guitar was in the higher registers anyway, chords and melodic lines. occasionally i could use a lower D or C, but it was so infrequent - and such a chore to "ignore" that 7th string - that i eventually sold it. my musical knowledge also wasn't that great, so the extra notes really didn't mean much to me. i could barely improvise a basic solo with basic shapes, had to memorize any solos i played. i was good with chords for improvising or sitting in without rehearsing, but i didn't really know how to incorporate the 5 lower notes at all.
for the past 7 years or so, i've been playing solo and duo acoustic style cover song gigs. it has pained me as a solo guitarist that the lowest D note is the open string. compared to even a C on the A string, it sounded so thin and not full compared to songs in E, G, A, etc. i play floating trem guitars, so retuning to drop D takes time and i don't want to do that. (i've tried all the trem locks, but don't like them). i also don't like using effects/pedals for the primary sound of my guitar, so no octave effects or pedals. i want people to see one guy with a guitar, and that's what they hear. (this is generally speaking, and just my concept of a guitarist for myself. many friends use all sorts of effects and sound great!)
i've been listening to Animals as Leaders for a while now, and the 8 string guitar concept - where the lowest string is another E - sounded so intruiguing to me as an "acoustic" player. i also remembered from my previous 7 string experience that you could play a nice D chord with a similar shape to an open G, and get that lower D note to sound full. my fretboard knowledge has improved a bit over time as well, and the frets actually became notes to me, rather than just positions and numbers. so i decided to give 7 string another try.
i got the guitar, and yup - it immediately was a pain. the 7th string was "in the way" constantly. i felt i couldn't play my 6 string stuff anymore. string spacing/position is slightly different as the neck is a bit wider, i kept missing the string playing in the middle of them rather than hitting them like normal. aside from that big D chord i described, or a Bsus2 chord, i didn't know at all how to use the low string. i was right back where i was in 2005.
but i decided to change my view on the guitar. rather than seeing it as a regular guitar plus one string, i approached it as a different instrument. sure, i was familiar with 90% of the fretboard (the 6 normal strings), but i approached playing chords "from the 7th string first" if that makes any sense. i may not be playing that low string in a chord, but i visualized the chord from there first.
just like playing an open A where you mute/bypass the low E, i visualized an open E the same way. F#m, G, etc. same thing. we've been playing guitars where the E string is the lowest and "nothing is in the way" and "no string to skip over" forever. so it's just a new habit that needs to be formed. once i got my "E string" chords down that way, i then moved to the "A string" chords. this was more difficult because i had to "skip" 2 strings now. all i did for these chords was have my left hand off the guitar, then naturally put it on and immedately hold a chord. often it went slightly to the wrong place. but in just a short amount of time of this type of practice - which seems silly of course - it felt more and more natural.
another huge problem was i was so used to using my thumb to fret notes in certain chords. D/F#, some F#m chords, sometimes an F note for an open Fadd9 where i can't bar the 1st fret, etc. with a 7th string there, i have to either stretch my thumb much farther, or learn to fret the chords differently. i tried the stretch thing first, as it was major habit, and it didn't work too well. so my D/F# and other chords now use fingers and no thumb. this took a while to reprogram, but it's pretty quick now. but this made me realize i can thumb some of the 7th string notes. i'm still working on this, but i can play a standard open C, and put my thumb on the first fret for a low C now. slide up 2 frets and you get that fun D chord, now with a low D. lately i'm trying to learn standard chord shapes incorporating the B string. i can do a basic minor triad now while muting the E string, but it sounds super plain. still, i have it. exploring other "new" shapes as well.
i can also do a good number of Drop D songs (or other lower tunings) without changing tunings at all. it's voiced a bit different, and i may have to jump around the fretboard a bit more than with a Drop D tuning, but it's possible and sounds good without tuning or having a 2nd guitar.
many people drop the B string to an A for a "Drop D" approach to those strings. personally, i don't want to do that though. i do like how you can hold an "e string" chord and the 5th is under it on the B string, but i don't like that notes are "2 frets off" with that tuning. that puts a D on the 5th fret instead of 3rd, and i can't play that open D chord anymore, and would be forced to play a 5th fret "a string" D instead. also, almost all my gigs with other people are never rehearsed. i need to have command of my instrument and know where things are so when my partner calls a song, i can just find the chords using my ears. this is mostly why i never use alternate tunings, as i need to be fast to find the chords while i play a song for the first time. so the 7 string drop A thing won't work for me. if i played more rock stuff and it was rehearsed, i could drop the A most likely. but for "standard chords" and music, i find that the standard tuning works the best.
i think it's common to get a 7 string and "ignore the 7th string" for a while, and just play what you're used to. i think this can work eventually. but ignoring the string just means you never use it, which means why do you have it? it all changed for me when i approached all chords and notes including the 7th string, even if i didn't play it. that really made it come together for me. many habits had to be unlearned or changed, and new things in general had to be learned, repeated, learned, etc. the 7th string is an "also" not an "instead of."
for the solo/duo acoustic thing, i really, really like having that 7th string there. it's only 5 more notes, but i try to use it as much as possible. even just basic things like having a low D to go to while in the key of G just makes more sense when improvising chords or melodies. now my "problem" low notes are a Bb and A, as the open A is the lowest A i can get. that's still low enough for me to sound full, but i do wish i had those notes (but won't "drop A" to get it like i mentioned). but that's totally ok.
when i pick up my 6 string now, the neck seems SO small haha. because of the slight string spacing/position difference, i do have to practice on it from time to time. but the transition between the 2 isn't that big of a deal really, now that i'm familiar with the 7.
if you're just doing "lowest string chug" types of things, i think a 7 string will be easy to transition to. the intervals are generally the same compared to a 6 string. if you're playing "classic" rock riffs and songs which were designed around what a 6 string offers, you may never find a need for the 7th string just because it was orchestrated on a 6. even substituting notes to the lower octave, it may even sound wrong since these types of songs are so ingrained in our minds. in these 2 situations, the music is orchestrated for the guitar, so using a 7 string guitar may not have any relevance as those extra notes are nowhere to be found in that music.
if you approach guitar and music in a more general manner though, this is where i think an extended range guitar can be a benefit compared to just tuning a 6 string in an alternate way, or just lower. with alternate tuning or lower tuning, you're still performing songs orchestrated on that instrument. majority of Drop D songs are performed in a unique way because of that tuning. low tuned guitars are the same intervals/orchestrations, just in a lower tuning.
when i play songs, they're in different keys, i or my partners may perform them in a different way from the original orchestration, and with that, we simply need the notes, not the specific sequence/orchestration to perform the song. so we just need the chords in general, and not the exact original way it was orchestrated on the instrument. that's when the extra notes come in handy for me. when i play guitar, i mostly am not playing from memory. it's a more "in the moment" thing where i know the chords i need and grab them as i feel right then, rather than "this is how the song goes, play it the same way every time." that's just my approach, of course nothing wrong with rote memorization! so having the notes available is nice if i'm feeling those lower notes in that moment.
i'm by no means an expert on 7 string at all. but i'm at a place where i'm very comfortable on it, can incorporate the lower notes often as needed (but still learning!), and do prefer having it vs a 6 string. it just takes time and maybe coming to terms with why you want a 7, and if it fits in with what music you're performing.
life story, sorry. but that's where i am with the journey so far.