I think all domestic relations should start as FWB. Sexual compatibilty is critical in any LTR that isn't Platonic. I've seen too many unhappy relationships that failed due to sexual incompatibility. One of my father's wives tearfully told me a month after their marriage, after moving in to our house with her daughter, that he just couldn't satisfy her. As a 15 year old, I wasn't sure what she meant (late bloomer). If they had had sex before marriage, a lot of grief would have been spared, and I wouldn't have that memory still, well after they are all dead. Unless you regard sex as a procreation thing, the pleasure derived from sex should be shared, emphasis on sharing. When it's with a friend, someone you really care about and who cares about you, it's magical, nirvana. That's why it's referred to as making love. That's how friends become happy spouses, lovers, whatever.
Being a friend already is a benefit. No person can tell you what to do. No judgment is necessary or needed. There is no shame or blame when someone is giving or receiving gifts. I am a friend of many homeless people and I give to them as much as I can. There is no reason why you can't receive gifts from a person who cares about you. I love giving and never have attachments on what the receiver does with my gift. The best gift I can think of for myself is a person who accepts my gift with grace and shares their happiness about it.
I think it depends on the person some can and some can not
I tried a FWB situation a while back and to tell you the truth a stopped it pretty fast because the intimacy was shallow,cold,and left me feeling empty as in that type situation your not supposed to have deep feelings for that person,its more about self gratification than pleasing someone you love,and in my case the female was married he did not know what she was doing and according to her he could not have a erection due to some illness he had so there was that guilt of doing harm to some guy i did not even know.The whole situation to me was a waste of time and i would never do it again.But again there is some people who would find it a perfect fix for them.I guess thats why we should respect other peoples opinions and feelings let them do whatever they like do not down them for there choices and concentrate on you and how you feel and what you truly want.