Friends with benefits

Y open with boring stuff? No use in that...
Friends with benefits... What does this mean? Does a "normal" friendship have no benefits "attached"?
And why is sex a benefit while, for example, companionship is not?
I'd say that a friendship is full of benefits. Or, in other words, a friendship is beneficial for those people involved.
The so-called friends with benefits have sex (some don't, ahahah). Maybe the occasional meal together. They do have some benefits. But probably not those of a real friendship.
So Y not call it "Sex with benefits"? I mean, it's usually more than just casual sex. It's something that lies in that grey area where everything that we can't put a name on goes.
As for me... I'll just leave a word of advice: don't mix friends with sex. No benefits in that!!!