Just found an article that may help explain a little of the difference in using flat pedals vs. clipped (I say a little as this test didn’t test flat pedals and does not take into all the goals of pedaling a mountain bike which include confidence and control).
The article is worth reading but here is what I found interesting:
“In a 2007 study, Korff et al, looked at the effectiveness/efficiency relationship of four different pedaling techniques: pedaling circles, “stomping,” the riders own self-selected style and the classic “pull up” through the bottom of the pedal stroke approach.
Their study established that mechanical effectiveness is greatly enhanced by using the “pull up” technique; it ranked higher on an effectiveness index than pedaling circles, self selected or ‘stomping’ the pedals. Gross efficiency, on the other hand, was significantly lower using this technique. It took more energy to use the ‘pull up’ technique than to simply pedal in circles or stomp. Unfortunately, Korff et al, didn’t delve into the efficacy of the trade off. Is it worth the decreased efficiency to get the greater effectiveness?”
Which to me means clipless pedals might be a huge advantage in loose and or steep climbing sections as you can produce more power. The reason I mention loose conditions is often a hard downward pedal can cause you to spin out. I tested this yesterday on some steep and loose sections of trail at Bootleg Canyon and realized that I use a completely different pedal stroke in those conditions than any where else. When it is steep and loose (or just really steep) I use a lot of upward pulling that I don’t use any where else.
The article, which also backs up my theory that just because a high cadence works for Lance it might not be best for you can be found here: http://www.pezcyclingnews.com/?pg=fullstory&id=8076
Again, don’t just agree or disagree with the article, experiment, find out what works for you.