My band does a half dozen "acoustic" gigs per year, complete with three-part vocal harmony. It is amazing how full we sound. I use a p.o.s. Hohner. I paid about $250 used and I have never regretted it. Sometimes people don't want a 5- or 6-piece band with drums, p.a., etc. We generally make the same money per man (or more) playing acoustic.
A third practical application: you hear a song on the radio, you run to unpack your electric, find a cord, plug in the combo amp, and try to play before the song ends. Or, you just pick up your acoustic.