Either there is, or isn't a God. Pretty simple isn't it, really?
The way that I figure it, in simple terms is this. If there is no God, and yet you believe, no harm, no foul.
If there is a God, then you are on His side, and you have the blessings that he will give.
What possible harm is there in believing in Him?
My personal belief goes much further than my example, but that is between God and myself.