For me, the only reason that I would even begin to think about not covering my pool is because a cover costs money.
Other than that, there is no reason not to. It takes me all of about an hour to winterize my pool. The cover keeps everything out of the pool. I take any water off the cover as it collects. I remove leaves from the cover as they collect. That really is not a big deal. 10 min a few times a week.
When I open my pool, it takes about 30 min to remove the cover, clean it, and store it. I honestly could open my pool, and not even SLAM it. I opened this year to clear water, with 1.5 PPM of CL and 0.0 CC. I SLAMed it anyway, just to be sure, but it passed OCLT with no issues.