My current band don't, and we dont feel the need. our PA 1x15 speakers have a nice low end kick, which helps the bass drum punch through the backline and over the heads of the crowd, but we dont mic anything else other than that and the vocals.
I think we would have a better quality of sound/mix if we did use them, but the added expense/weight and space needed are outweighed by the fact that we dont 'need' them as such.
My old band used to use just one of those Peavey powered Subs, but again, space constrictions meant it got left at home or often than not. We used it for functions but not the social clubs.