This is good advice and will work as described.
That said - I don't do this. My FM3/AxeIII is sending my signal at the volume I will keep it at, as soon as I power it up.
I will keep my guitar volume low and ease it up while a sound engineer dials me in. But I always send them full volume.
Any sound engineer should have your channel (slider) all the way down and channel muted, until it's time to check your line.
When it is time, they should ask for you to play (full volume) and adjust the input trim BEFORE even touching that channel volume/slider.
After they set your input trim, then they can bring you up in the mix using the fader/slider.
If they don't set your input trim properly, then yes you can blow some speakers. If the engineer doesn't adjust the input trim before putting you through the PA, then they are not competent, and let's hope they have a limiter in place.
This is the same process for every instrument plugged into a PA. Any instrument can blow your speakers if you don't know how to operate your PA.
And I'm not perfect. I have smoked 2 sets of tweaters by having a feedback loop that I couldn't get to quick enough. Live and learn.