Did you watch any of lifecoach's slay the spire streams? He has some very impressive win rates/streaks and is I think much more conservative with potion use than most players.
In slay the spire, both HP and Potions are limited resources, so throwing a potion to save HP is not necessarily a wise decision if you're at a low risk of overflowing your potion inventory and won't save much HP. There's also deck dependance here where you CANNOT win certain fights with your current deck without having a certain potion saved, but you CAN survive the fights until that fight without using potions with minimal to no HP lost.
The better analogy in this case is the resource gold, where it's usually a trap to pass up buying a useful item in order to save your gold for a better once since that will cost you HP on average/will increase your variance of HP loss and end runs. There's items in the game like "Maw Bank" which generate gold each floor until you spend it at a shop which tempt your monkey brain into dying halfway through the game without having visited a shop once. While saving potions for half the run happens regularly, saving gold for half the run tends to end poorly.
He's playing Watcher. But yes, to maintain his high winrate he's optimizing to mitigate bad rolls
(re Watcher, I'm not saying his results aren't impressive, but its not comparable to the original 3, see first run of https://www.youtube.com/watch?v=2xLmKGqwAIU where baalor wins vs heart using only starter cards)
