Someone once described clipless to me as giving you a 10% boost when you need it. That wasn't based on any scientific measurements, just his feeling. It seems sort of correct. I don't notice much benefit when I'm just cruising along. Accelerating hard, sprinting, or climbing is when it helps me the most but as far as getting to work faster it doesn't make a real difference (for me). I like them enough that I wear them commuting but if I were forced to go back to platforms it would hardly be the end of the world.