I believe everything about what will happen in our lives is already set in stone--we just think we've got free will (and that illusion is good enough for me). So to me, prayer more of a comfort thing.
lol predestination.
Predestination is scary. Specifically, if predestination is true, then what's the point of religious people attempting to convert others? Well actually if that's the case, and it has already been decided who is going to heaven or hell, then what's the point of any of this?
Anyway, I'm not a believer but prayer does seem to help people and make them feel better. Never helped me out, but if helps them then they ought to go for it. Whatever works.
If you embrace Calvinism, and then get rich (a sign that God loves you), that is advance notice of where you will probably end up after you're dead. We all love hints about what the future holds. I hope that helps.