Both main characters are good people who are genuinely best friends. Kunis and Timberlake have excellent chemistry and are hilarious as a duo. Great lines for both of them- great writing.
Even the deadbeat mom loves her daughter, and the daughter forgives her. The mom isn't a great parent though (suggests doing drug as bonding and references casual sex as a lifestyle)
The second half as Common Sense says does talk about staying true to yourself, loving yourself, letting yourself be loved, taking care of those you care about, and standing by family. Great messages there and it ends happy.
There is a lot of sex- discussion about oral sex, oral sex that while not seen outright is seen under a blanket, moans, discussions about orgasms as well as characters reactions to doing so, naked backsides by both characters, casual sex in multiple places. I didn't think it was overdone personally; both characters are funny and have great lines even during the sex.
Hilarious film, genuinely l laughed aloud. The characters are genuine and believable.
Drinking/partying is displayed by adults.
Swearing is common- main characters swear often.
Romantic Comedies are trashed often.
Honestly, friends with benefits is an issue for teens these days; I'd let most teens see it, its an issue they are familiar with. While the main characters are adults and perhaps more mature about the situation, would be enjoyable for teens and impart some positive messages towards the end.