i second the carrying multiple weights recommendation.
mold dictates stability much more than weight, but often you want subtle stability differences, such as when you absolutely positively don't want to turn the disc over but you still want a straightish flight or you want the disc to hold the same line but fade sligthly earlier than usual, moderate winds, etc.. heavier discs will fit that bill.
imo, the best rocs started out 180g and got beat up to the point where they are now 175g
