Tommy, the first course that popped into my head when thinking of rear bunkers was Chicago. I just counted a full 12 (!) holes have a back bunker (1,3,4,5,6,7,8,10,11,13,14,15) and the first time I played out there I saw my fair share.
Aside from places that have safety concerns where a back bunker may catch errant balls they can also serve as a backdrop a la 13 at Cypress. Lastly and I think most importantly they can be used as a deterrent especially at a members course where just knowing there's danger back there makes you question your club choice.