What Orithan said; passive regeneration is dangerous because it encourages passivity. If the optimal strat is "wait in a room for a minute to have full health", the player is stuck with the sadistic choice of doing the optimal play and being bored, or doing the risky thing knowing that you're sabotaging yourself. When designing systems, you should always ask yourself "is the most efficient way to play this fun?", because players will optimize the fun out of the game if given an opportunity and even if that doesn't take hold during a first playthrough, it will affect replayability.
Hollow Knight does an interesting idea adjacent to this; you have a soul meter that is used both for casting spells and healing, and you only get soul from attacking (or using a slow midgame item on enemies). Whenever you attack with the spells, you rob yourself of potential healing, whcih makes casting spells seem scary when you're not good at the game, but as you get more confident in your ability to not take damage, they become efficient ways to deal with things quickly.