Safewords can be a bit of an annoying anti climax if overused sometimes, BUT, I think they're pretty much an absolute "must" for most sessions because the respect and trust you place in each other during a session is huge. I probably wouldnt play without a safeword unless it was a regular lee and friend, and she told me categorically she wanted to try something more extreme. Even then Id be hesitant and constantly checking them.
I finally broke one of my most regular lees last year and it took me some real doing but once I heard the safeword, she honestly looked broken bless her. Was nothing but cuddles for next hour to come back to ground level because it meant that the limit was hit. If id carried on, and we hadnt had a safeword, it would have ended up in tears no doubt.
The safeword is super frustrating when you find a good spot and its just shouted every single touch, but regardless, if you agree to play, you gotta respect it. I had a lee last year who must have safeworded at least 30-40 in a few hours anytime I touched her feet 🤣 which is a shame because she had great feet to tickle lol