There's no reason NOT to use clipless if you like them, but I've tried several systems over the years on many different bikes, and at least for me there's no advantage. I've done the same 25-mile commute 75-100 times a year since 1979, plus thousands of other rides, and there's no difference at all in my average times with platform pedals (no clips), with toe clips and straps or among any of the three clipless systems I've tried. My fastest time home from work (500 foot gain in 12.4 miles) came on an old Trek touring bike, with rat-trap pedals, toe clips and loose straps, on 700x35 tires at 80psi. It was just a good day, I was in decent shape and hammered all the way home. That mattered more than the bike, pedals or tires.
Contrary to popular belief, studies have shown that almost nobody pulls up consistently on the pedals, or truly pedals "in a circle," as experts often recommend. They can measure pedal force with strain gauges, and it just doesn't happen except for a few strokes during sprints. A lot of what you hear and read is unsubstantiated by evidence. Grant Petersen at Rivendell claims to be just as fast with BMX pedals as he is clipped in, and I believe it.