You have got to play the back-ups either in blow-out losses or blow-out wins. These guys need to get some reps and also like someone said, the starters need to stand on the sidelines and get some perspective when you are getting killed. I live in Phoenix, and although a different sport, the Phoenix Suns come to mind. Back in the early 90's we had a coach who would play a second squad of 5 even in crunch time to give the starters a rest but also to have quality depth. Then our coach a few years ago, only played 7-8 guys the entire game. When a starter went down or the front 5 were gassed, we were dead. No experience on court and we couldn't afford to have any of the starters out for more than a few minutes.
I don't understand a coaching staff who won't give time/experience to its players, starters and back-ups. Back in the TO days, we would have our starters out of a game by the 2nd series of the 3rd Qtr. Of course, we were good back then...