This is the forum for helping you out if you're stuck or if you want to discuss the nitty gritty details of the dungeons within Mount Grimrock. Warning: forum contains spoilers!
Not entirely useless, it will mean about 25% Poison + Cold Resist. Mostly the former is decent to have.
However, it's only 15 extra HP, and your remaining points pretty much have to go into DEX... well, I wouldn't want a -4 to hit anyway.
Personally, I'd do 20 STR, 11 DEX, and leave VIT on 14, but that's just me.
On the other hand, I've only played normal, so maybe that HP is more valuable on Hard.
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I think it depends on how confident you are about your dodging skills. I beat the game on hard with 16 vit on my frontline fighters and apart from a few unlucky 1 shots by ogres I didn't have any trouble. Spells are pretty easy to dodge when you make sure you fight enemies on your terms.
Unless they're lying to us vitality/willpower also increases the amount gained pr level, dunno by how much. However I had a 20 vit mino and 16 vit human fighter. The mino ended on 211 and the human on 196 hp (without any equipment influencing it). I know I leveled athletics to 5 for the +2 vit early on the human, but don't know how much of a difference that made.
All in all if I could change it I'd smack it all into strength and dex. Missing is the biggest problem and on hard you can't stand toe-to-toe with anything but snails without getting a royal beating. With all my vitality even at level 13 with full valor they got pretty much oneshot by ogres, so vitality on hard.. Meh. Get dex/str and learn to 2x2 them, and it also increases the evasion. If you get hit you're done either way.
Something I've noticed is that HP gain when you level up is random, so if you save right before you level, you could maximise your health/mana gain by reloading until you get the max HP gain from the level up.
Max gain per level (+7 HP) starts at Vitality 18, so no in that regard. Anything over 18 is however quickly gaining you resists, which you can consider being somehow beneficial, I wouldn't.