I ride clipless now, but I used to be a staunch platform guy. Developed problems with my knees that are caused by tight hamstrings and generally poor tracking. The physical therapist who fit me on my bike recommended clipless so that I could get everything positioned correctly. I still have to do some exercises to keep my legs tracking straight, but now at least my feet stay pointed the right way so as to minimized knee problems.

All that said, since changing over I must admit that I much prefer riding clipless. Although you loose a bit of convenience and the cost is greater, i love the secure feeling, consistent power and the stability. Clipping in and out of SPD cleats hasn't been a big deal. I'd probably change again without knee issues, just experiencing the difference. But if you like platforms and they work for you, by all means don't fix it if it ain't broken.