Friends with benefits?

So I'm currently friends with benefits with this guy, but I know a lot of people, including some of my friends, disagree with the situation. As far as I'm concerned we both know where we stand, and even though we're not dating we're still close, we're comfortable with each other and can talk to each other about anything. I just wondered what everyone else's opinions were on friends with benefits, and why you agree/disagree with it. *it won't affect our relationship in any way I'm just interested*