I format every month. I have 2 hdds though. 1 ssd and 1 sata drive. My ssd has my games and my OS on it. And then whenever I download anything, I put it on my sata drive. I format the sata drive every month. But I defrag, disc cleanup every week, and virus scan and such every other day.
My computer is cleaner than.. well.. something that's very clean.