This is never a good idea. Players need to measure their desire to give 100% effort with the knowledge that sometimes, they need to back off in games that don't mean anything. In 2004, the A's Mark Ellis suffered a torn labrum when colliding with teammate Bobby Crosby in a spring training game; Ellis missed the entire season.
Upton is now paying the price for this collision, in which he hurt his back:
#Rays Upton says he's going on DL to start season.— Marc Topkin (@TBTimes_Rays) March 28, 2012
Upton hit .243/.331/.429 with 23 HR, 81 RBI and 36 stolen bases for the Rays in 2011, although he's never quite gotten over the hump to the superstardom forecast when he was Tampa Bay's No. 1 pick in 2002; they'll miss that bat until he returns.