There's really no need for all of this anecdotal discussion. Last time I had access to some research databases the available peer-reviewed literature indicated that an extremely skilled cyclist (i.e., world class) picks up a percentage point or two in cycling efficiency when attached to the pedals. The fact is that the bicycle drivetrain is an inherently efficient device for the transfer of power. Attaching yourself to it doesn't add that much. On the other hand, clipping or clicking in certainly adds to riding experience for meany people and it provides employment to a lot of designers, manufacturers and retailers. Feel free to do it.