Most courses around here have Blue, White, Gold (sometimes), and Red. Once in a blue moon, if I'm up to it and the course is relatively empty, I'll play the blues. 98% of the time, I'm playing the whites. If I ever dip down under 10 or so, I'll consider moving back a set.
To take this a little bit OT, I see guys way worse than me playing the blues all the time. Guys who I would be surprised if they are shooting under 90 (or 100 even). In fact, when I played Monday after work there were two guys in front of me hitting short, off line drives, followed by shitty second shots, from the blue's! I can never tell if these guys are doing it for kicks, or if they legitimately think they have the game to play from the back tees. I was walking (they were riding), and I was pretty much on their ass. Wasn't even playing that fast either. Hit some practice balls, practiced putting, still caught them on most holes. /rant