This is a very interesting ability. The feat comes with two spells, one to sacrifice pet points one at a time to give a 4 hour boost to all of the Necromancer's magic damage by an amount dependant on your level, and the other reverses the process one point at a time. It takes about a minute or so to get through all 8 pet points either direction, plus whatever time it would take you to re-summon your minions after you turned it off. Sacrificing pet points also adds a debuff to your pet damage output.
With all 8 pet points sacrificed, the magic damage boost is strong enough to make the DPS output of a Necromancer's attack spells a pound for pound match to those of a Demonologist, if not better, effectively transforming the Necromancer temprarily into a Frost or Unholy Demonologist, interesting counterparts to the original Lightning or Fire kinds. This opens up a great deal of tactical variety available to the Necromancer as the situation demands it, especially since the Necromancer has more-or-less better crowd control abilities than the Demonologist.