Are you talking about "friends with benefits"? I can't imagine that'd work out well for long. Too easy to form an emotional attachment where physical intimacy is involved. The more such intimacy, the greater the likelihood of such an attachment. If you're looking for that, great. Just don't expect it to be neat and simple and confined for long.
DISCLAIMER: I could never do the whole FWB thing. Just not my cup of tea.
It can actually work out pretty well
Trust me, just gotta find the right ones.
But yes it can defiantly turn out bad too!