why is it we dont use floats with inground pools?
would water runoff off the tarp be better then it filling up with water?

total noob question, just curious

You can certainly use one, if you'd like. It won't hurt anything and can help you keep the cover water free. However, possibly the main reason of having a float under an A/G pool is to keep the weight of the water on the cover from pulling in the top of the wall (which which you have no issue)

would it be better tho to have a float?
i live in a very vegitative area, pines and decidous, which will drop alot of leaves
i would think it would keep them from getting in the depression and thus the pool water

If I were going to cover my pool with a solid cover instead of the lock n loo that I have I would use the float. It will keep water and leaves from gathering in the center of the cover pushing them to the edges of the pool where they will be easier to clean off.

you would have to have the cover stretched pretty tight in order to all the water to run off. if there is any slack then the water would start collecting there and before you know it it will pull the cover down to the water level in the pool.

i have a fence around the pool
i planned on tying the tarp to the posts

unless it's absolutely smooth with no sagging, the water will find the lower spot, accumulate there and collapse the fence if it doesn't, then the snow&ice will since snow&ice will stick to the tarp even if it's perfectly stretched.

i toyed with a similar idea last winter and decided it won't work. but i hope i'm wrong and you post back in the spring telling us how awesome it worked!