I would like SA to always apply, with a quick way to switch it off in case you're trying to finish off something with 1hp. Having to confirm a reaction prompt every time just because on some rare occasion you might not want it to happen is a bit much.
I've mainly had sneak attack just set to auto-trigger (ie without asking) in the reaction system and haven't noticed any problems. I generally don't bother even turning it off for low HP enemies, as if the enemy is killed by the initial weapon damage then the sneak attack damage doesn't trigger, and is automatically saved for another potential attack in the same round. If I did want to turn it off, I could just click the (admittedly small) reaction icon up at the top right of the quick bar to open up the page that would let me adjust the settings. Which isn't superconvenient, but as I've not had to do it yet except when I've wanted to set sneak attack to "Ask" so I can test it properly, it's good enough for me.
