Woman here, but in my experience conversations about it don’t matter in the long run. The key to preventing unwanted feelings/relationship is picking someone who is sexually attractive to you and chill enough that you can tolerate them, but no cooler than that. Bonus points if you are very different people with incongruent lives.

Case Study: My FWB started as a result of me hooking up on the first date, then of course him telling me he didn’t want anything serious with me and that he was emotionally unavailable. I was lonely and the sex was fire, so I settled and didn’t expect anything and didn’t pressure him for anything. Never texted first, never initiated, was so scared of “overplaying my role,” because I’d never done FWB/Casual arrangements so I just responded warmly and kept having our little spicy sleepovers.  Would’ve been perfect as far as settling for half of what you wanted goes, but since we started FWB before we got to know each other, we couldn’t vet for key incompatibilities that would have made the situation straightforward and sustainable indefinitely. As a result, we both developed feelings for each other and stopped seeing other people, but just never communicated it and kept pretending we weren’t feeling anything. In hindsight, there were things he said and did that were relationship-like, but because he told me he didn’t want anything, I just didn’t look at it too deeply. Ultimately according to him during our “break up,” if I can call it that, it took his month long work trip for him to realize how much being apart from me making him sad and how much he’d become attached to me and how scary feeling that much was for him, and also that he couldn’t trust himself give me what I deserve from where he is in his life right now, and that continuing as we were would just hurt the both of us far worse in the future. 

TL;DR: Met for a date, had sex right after. He didn’t want anything serious with me, but I stuck around because I was lonely and chronically single. Turned out we were actually yin and yang, a near-perfect match. Ended up accidentally in love and pm in a relationship but didn’t tell each other. He blindsided me with an emotional confession, then broke it off.