Of course it's opinion. And who says you don't need to defrag on OSX? When you're low on space, a defragment will surely increase performance.
But, doesn't defragmentation process itself requires some free space to move the fragmented files into? OSX inherently allocates space in such a way that fragmentation is minimised.(compared to XP) But, I think it would still require defragmentation after a period of time.
I use Windows XP, and am quite happy with it, because of the wide range of applications it supports.
