Seriously though,mostly what rocktheEPs said...but it also depends on the ski, a fatter ski that you might need more leverage to lay on edge, you might want them. Honestly though, with most people, the difference is so marginal that you won't notice it, unless your gear is 100% dialed, it won't make that much of a difference.
"Nothing is impossible. You are only limited by fear and even that you can overcome."
"a simple equation:
force of impact + force of steeze = 0
the two negate each other. for eric, stomping a 60 ft cornice switch is like jumping on a really soft hotel mattress." - ChronicF explaining why Eric Pollard still has knees.