It's completely a matter of preference. I'm saying that as one of the few people I know of that is perfectly comfortable switching back and forth between a quality platform, and clipless. Most people who really really feel the platform is better will tell you it's because they don't have to take time to unclip when stopping or going through something technical and taking a dab, or putting a foot down in a fast turn - other's will tell you that proper technique with good pedals and good shoes will get you roughly the same pedaling efficiency, and still others that you shouldn't be pulling up anyhow, all your power should be generated pushing from the hip.
Clipless advocates will tell you they are more efficient, and you can generate more power with them.
From a personal stand point, when I'm really out cutting up, I like the additional freedom of movement platforms give me. It's not that under normal riding conditions I NEED more float than my clipless setup offers - it's that sometimes it's fun to throw the bike around in ways you simply can't if you're clipped in. I will say that, yes, on my single speed, certain sections of the trail the require more power are easier to clean clipless, but there are very few places I can't clean on either type of pedal, be it technical, or just steep.