Depends on the size I suppose. You can.....

I wouldnt do it.
1. Convenience - if its a pain in the neck, how often are you really going to do it?
2. Protection - The reel neatly rolls the cover up and the cover doesnt drag on edges or the ground. If you cut the cover's life in half or a third then you end up paying for a reel in the long run. (Good for the guy selling covers I suppose)
3. Keeping the pool clean. Not sure about your yard but I'd drag leaves and junk around if it wasnt on a reel.
4. Storage. The reel rolls out of the way neatly next to the pool when you need it. leaving the cover in a clump or folding it up is ugly and again inconvenient.