why do people say to not upgrade your nail, even when it still makes bosses require less hits?

[Hamsternick]

i wana know

[Perseus]

Some bosses' health changes depending on your nail level.
Like you say, having a better nail always means you need fewer hits to defeat enemies and bosses.
However, your spells deal damage independently from your nail level.
So if you have powerful spells but a low-level nail, those bosses take fewer spells to defeat.

I don't know why people would say that outside of the context of a challenge run or a speedrun, though, since most of the bosses affected are Warrior Dreams, and they're among the easiest bosses in the game.

[Fingusa of the East]

Yup, as Perseus said there are a bunch of bosses in the game that have scaling HP pool depending on your nail upgrade. Some bosses scale a lot. Like, ridiculously so.

Spells do not need nail upgrades for scaling of damage and with certain charms and low nail upgrades, they can melt bosses in a few attacks. It is actually ridiculous to see and experience.

Since normal enemies and early game bosses are not really an issue, depending on how you wanna go through the game, not upgrading your nail and focusing on spellcasting could be much more valuable to you as otherwise spells kinda become meh from my experience.

[Nibbie]

Found a chart on the wiki of damage values and enemy health for some specifics. For example, Gorb has 200 health if you haven't upgraded your nail, and 320/479/570/640 health for each nail upgrade, so a bit less than triple health at max nail. Considering the nail damage goes from 5 to 21 at max, upgrading is still ideal and will result in faster kill speeds (40 hits vs 31 hits at max), unless you very specifically use a ton of spells instead (two Shaman Stone Abyss Shrieks kill him with no nail upgrades, for example), and you also have to not care about the other 98% of enemies in the game who don't scale at all. That strategy is pretty much just for speedrunning those specific bosses (only 12 of them that scale this way), there is no reason to do it in anything resembling normal gameplay.