Free will is a case in which something like Pascal's Wager makes sense. I behave as if I have a free will, because if there is there are consequences depending upon how I behave. If I don't have a free will, then this is how I would have behaved anyway. There's really no downside.
If there is a god, I want to believe that there is a god. If there is not a god, I want to believe that there is no god.