I tried leaving the crusts on a little while ago. I kept them almost completely dry for about two weeks and it felt very unsafe. It seemed that the crusts grew thicker and went deeper into my skin. Based on how thick and hard they were i knew there was no way they would come off on their own, it felt like the crusts were becoming my lips themselves. When i wiped them off with a wet towel they hurt for 2 days after. And were alot hard to wipe off the usual.
I've given up on leaving them on and now just lightly exfoliate and moistarize before the crusts even have a chance to grow back. For me its the best way to maintain them. On the good days they actually feel like normal lips. If you are leaving your crusts on id recomend sniping the pieces that come loose with small sissors, its alot better then impulsivly peeling of the entire thing, as im sure many of us have before. I also wouldn't recommend letting them dry too much because despite what other people have said, and what i had previously thought... that the crusts are trying to heal, letting them dry too much for too long can be quite painful and damaging.