Guess nobody knows, Ed ...

It depends on the people, sometimes its as easy as it sounds, other times it gets complicated or leads to some sort of relationship.

I've had "FWB" -relationships which have been wonderful experiences... but it's going to vary from person to person and how well y'all manage to keep thing in perspective.

Are y'all FRIENDS first and foremost to begin with? And does that friendship take presidence over any other type of relationship (sexual or what) that y'all experience together? If so... then you've got the right idea. I've seen too many of these degenerate when one friend gets caught up in the idea of pushing it further and making it a romantic relationship when the other friend is only interested in the friendship with sexual benefits... like any other relationship (yes, a friendship IS a relationship) - it requires good communication and understanding.

You have to be able to walk away from the "benefits" portion of the relationship at any point if you're both not on the same page as far as the relationship goes... and maintain the friendship.

Be happy for one another if one of you starts "dating" someone and finds a romantic interest... support each other and ... just be a friend above all else.

...everything else is just "bonus"-time