In real life, that's not always the case. Hearts break, emotions flare and sexts get sent long after one party has sworn off the other. Even Kunis and her co-stars aren't fans of the concept.
"It's like communism -- good in theory, in execution it fails," she said in a recent interview with GQ magazine. "Friends of mine have done it, and it never ends well. Why do people put themselves through that torture?"
"For some people, yes," Patricia Clarkson said at the film's New York City premiere, "for me, not so much."
Motivations aside, the experience makes for some entertaining tales. ABCNews.com solicited stories from people who've had not so platonic relationships with their pals. Here, five of the best (or worst, as the case may be):
"I was coming out of a marriage of seven years and decided that a guy I worked with (who I had always had a crush on) and I should do a 'friends with benefits' situation. We 'dated' for four months. Our dating consisted of meeting at my house, motel rooms and talking on the phone. We did hook up a few times at work on a desk. I eventually realized that I wanted more and I deserved more. We decided to just go back to being friends, which was harder than it sounded. I just recently found out that he is now 'dating' someone else we work with. I'm glad I learned my lesson about friends with benefits; it doesn't work." -- Erin.
"It was freshman year of college. After grinding the evening away at Halloween frat party I found myself in my room with a guy who lived in my dorm. We had talked a few times before and I thought he was adorable the moment we met. Excited that we were finally going to hook up, I went in for the kill, only to be instantly pushed back: 'I think I might be gay.' Oh. That was not what I expected to hear.
"I retreated to my corner of the bed. Silence ensued for a solid minute. Panicking to get him to leave, I stuttered, 'Well, if you ever want to talk about it, just let me know.' The evening suddenly became a stock 'Oprah' episode. We actually did keep talking in the days that followed. Initially fueled by the desire to forget the awkwardness of the night, our interactions grew increasingly flirty. Then, one night while watching a movie, his arm slipped around my shoulders. The arm led to hand holding which led to groping which led to making out. Suddenly, my GBF had become my FWB. Things only lasted two weeks between us. While I was willing to look past his sexual questioning, I guess I just wasn't man enough for him." -- Francesca.
"It started during a Saturday morning class she attended with her mother, who was pursuing a bachelor of general studies at the same college. We were in the same study group (me, her and her mother) and though her mother was always present, we both seemed to get along fine. One Saturday afternoon after class, her mother had to run an errand, which left the two of us in the library. Conversation quickly took a different turn, since the library was just about empty at 1 p.m. on a summer Saturday afternoon. We talked about what we could be doing. We spent the rest of the afternoon between book aisles doing what friends with benefits do.