theres also some pokemon like most baby pokemon as well as golbat and probably others that evolve only if they like you above a certain amount at the time they level up, so if you want to prevent one of those pokemon from evolving you can give them a ton of herbal medicine just before they level up. there are some reasons you might want to do that, as unevolved pokemon usually learn moves quicker and sometimes learn special moves if you keep them unevolved up to high levels. theres also at least one item (eviolite) that only not-fully-evolved pokemon can use, it boosts defenses by quite a lot so it might be useful to keep something unevolved in this way if youre doing a weird strategy. however you can also press b while a pokemon is evolving to cancel it...so it isnt that useful to do this, tho theres of course a chance you forget to press b. but you can also have a pokemon hold everstone to not evolve. so its not that useful for this i dont think.

HOWEVER thats for playing the game the normal way. if youre playing with special rules to make the game harder, like nuzlocke-ing, then it can be useful as some of these rules restrict the amount of money you can earn. butterspeed nuzlocke rules (which i invented) mean you can't grind trainers or wild pokemon for money or items to sell, so your money is limited, and the increased healing efficiency of herbal medicine might be useful. one of the hardest special rulesets is nuzlocke with no pokemon centers, which means you can't heal your pokemon in any free way and have to rely on potions. in that ruleset the increased heal-per-pokedollar would probably be useful, but ive never played that way as it seems crazy hard. (no pokemon centers also means you cant restore pp, so you can only use a given move 5-35 times, less if its more powerful, and your only way to restore pp is a few pretty rare items, learning new moves, or letting a pokemon die and using another. butterspeed is just nuzlocke rules + no grinding.