I use one if I'm playing jazz. The band I play for has a repertoire of well over 100 songs. They use 3 different vocalists, each singing in a different key. My book for this gig is something like 250 sheets.
It very much depends on the genre and the gig. I spent a summer a few years ago playing on a cruise ship, just pop and party tunes, the usual awful stuff. That was all reading from supplied charts. There were four books, two red and two blue. The singer just called out blue 21, or red 14 etc.
A pub rock gig I'm guessing would look a little odd.