There is religion in my game, as I feel a world is usually a little empty without at least some hint of it, since throughout human history there has always been some form of religion. Also, since my game is in a fantasy setting, there is magic, which definitely has an impact. It allows for say, tribal religions, to provide their practitioners with some power, but doesn't necessarily imply that there is in fact any real spiritual being. When it comes to more organized religion, this also exists in my game, and as in the real world it is somewhat complex. What I mean by that is you might have people who are good people, but do bad things because they think it's what their religion tells them to do, or the opposite, people who aren't very good people but try to be due to their religious beliefs. The higher echelons of power within the organized religion(s) contain people much like those in life, people who truly believe, and people who use their position for political gain. Don't worry though, there is no pretend-to-be-good-but-actually-evil high priest in my game.
I'm not big on black and white characters, meaning the white knight and evil villain. Sure, some people are generally good, and some people are complete jerks, but almost everyone moves throughout that spectrum. I suppose that might seem off topic, but I point it out because people's behavior is impacted by the events in their life, and how they interpret those events, which is of course strongly influenced by their beliefs. In that regard, religion, even as a minor backdrop, can be a powerful tool in either plot, or in my opinion often more importantly, character development.
That's my 1.5 cents. (Not quite worth a full 2).