Wonder if there's a console command to eliminate the 1x per day limitation. I might actually use it for a change then.
TGM
Also removes shout cooldown.
As for me, I've only used Histskin once, but when I did, it was incredibly useful. Apparently it gives you 2x on your out-of-combat regen speed instead of in-combat regen speed. It'll keep you alive in a fight when you're battling some enemies while an archer chips down your health. I really ought to use it more.
Most useless daily ability is Beast Form though, without any comparison. No way of healing except feeding on already dead enemies, useless scare ability, worthless sprint power attack, a knockdown attack that does no damage, and weakened melee attacks. All for +100 Health and Stamina and a faster sprint. Terrible. Nowhere near as useful as the utility of normal-form (Dragon Shouts, magic,
blocking, potions, sneaking, archery, and various perk effects). Oh well. I suppose they needed
some form of gimmick to keep the wolfaboos and Twilight fans entertained.