i had it hit me incredibly bad once, but luckily barbs dont use it mages often or at all, much like their debuffs,(why take mana/debuff when another swing likely kills em anyways)
i guess alot of the reason no one skills it (besides the obvious reason of possibly ending a fight rather than causing a malus or debuff and prolonging their limited effective fully buffed state, is because of their damage potential to low HP or some not so effective defenses (ap multipliers) stacking dmg buffs and on and on..
but another reason likely is because it doesnt work like borrow, but removes whatever % of available mana you currently have, not total, though the time it was use was when I had full mana and setup with the most mana I could have at the time which was roughly 2900, and 40% just gone
not to mention a decent portion of HP
most times as a barb when I skilled it though, I hit mostly empty conjs it seemed so I dropped it soon. it is good in theory though with its low cd very close to ambitious, a conj can be be stripped of mana almost directly after sacrifice is off cd and cast again..but maybe to another class possibly, like knight since they have to use those debuffs and cant just rely on raw dmg.
off topic but id really like to see THESE spells worked on, not the ones we all know work, so many just sit useless in the trees for far too long (spell elude? that was a killer spell till they 'fixed' it to being an icon to pass by and nothing more. Brain piercing...another unique cool spell that was critical to fighting mages and stopping areas and such as it actually worked back then and out skills into cd..till it got 'fixed' too..)
maybe some can make (another) new thread of top voted most worthless spells/unused spells currently per class..maybe get some attention to some that need love..not neglected to focus on changing confuse for the 4th? time but still missing the entire reason it is imbalanced in the first place ..