I restart mine everyday otherwise it would get sluggish.
And I'd turn it off at least one whole day or night once a week just to cool it donw and give it a rest. I do alot of downloading, too.
go green. turn it off if you're not using it.
it won't hurt your computer but it will hurt the planet (not to mention your electricity bill).
I'm not sure what the OP is asking. I assumed he meant that his Mac was sleeping most of the time. Just to leave it running all day, every day, but not in sleep mode? Absolutely not for all the reasons above. But, to leave it on in sleep mode, that's fine. That's what I do. I never shut my Mac off with the power button.