The builder installed one of those overflow holes in the deck of my pool.

16x34 IG vinyl with a stamped deck.

2 questions, what exactly does it do, I pull the lid off and the water is about 2 feet from the top. and second, should I be draining it or let it be.

The pool is now closed and I was just wondering.

Oh, yea, I am in southern ontario and it can get pretty cold here for long periods of time.