Can someone who knows please explain to me what the two small holes in the rear cover of the smog pump are for (center of cover)?

I want to say they are relief holes but looking at the vane/rotor design I can't make sense of that theory.

I've recently converted a stock thirdgen pump into a vacuum pump and was curious whether or not it's something I need to pay attention to. In other words, I want to make sure they won't potentially reduce the total amount of vacuum the pump will be capable of drawing.