the problem is for long arenas, u are forced to get mana sacrificing HP more often, which is kinda anoying.
each time u use http://www.db.pandawow.me?spell=1454/life-tap, is like 100k hp less, so its kinda important to not get ur mana wasted because a bug
+ if u use drain soul, u lose 4,5k mana each s during 9s