i'll agree to an advantage in climbing, but good pedal spin/stroke can be accomplished through proper technique over purchased devices.
I've read several studies which utilized electro-muscle-analysis (my words; not theirs; i'm no physiologist) to conclude there is no change in muscle activity between riding clipless and riding clips on the flats.
Empirically, i never saw a gain when i switched to clipless, and never saw a loss when i went to platforms (on the flats)