It depends on how close you are as friends before you start having sex. With really good friends, but no romantic feelings, there is still emotional attachment, even if it's not as strong as if you were in a relationship. But with people you hardly know, of course there will be little emotional attachment.
I wouldn't exactly call it using each other either, but it depends on the situation. When you're good friends with a guy, I just see it as an extension of the friendship. No meaning? Hmmm, once again depends on the situation. I have situations where it's meant something, and I've had situations where it hasn't meant anything. It all depends on how close you are to the person in the first place.
Having said that, I don't have a preference. Different times suit different situations.