Originally Posted by
Carbonfiberboy
Efficiency is a red-herring because the definition is maleable. The big reason for clipless, and toe-clips before them, is that you use more of the muscles in your legs, hence each individual muscle takes longer to get tired. I.e. your legs last a lot longer and you'll feel better the next day.
While I agree with you, this is the very definition of "efficiency", i.e. using less energy to achieve the same result.