Here's my setup:
I use the FM3 for electric bass, upright bass, guitar for a cover band, 8-string guitar for my originals band, guitar in jazz combos, guitar in big bands, solo guitar, and guitar in musical theatre pits. For each of these, I have slightly different setups in terms of effects, scene usage, loopers, etc, and having one layout for each of those categories is nice. I also have many presets for each of those categories both because of FM3 CPU limitations requiring multiple presets for different combinations of effects, or different levels of reverb dialed in for different rooms, or for using different guitars or basses (I have my Strat patches dialed in differently than my Les Paul ones, different from my 135, etc).
All in all, about six layouts covers most of my needs for over 40 presets. Not having to manually program per-preset switches for every single preset would be much more efficient. It's bad enough that global blocks still aren't a thing on the FM3 (we had them on the AxeFX II over a decade ago!), so I'd rather not have to deal with another non-global annoyance.