Any disadvantages to running a vaccuum pump? (for oil)

Phreakish said

I'm glad someone else mentioned this. Actual pressure cannot and will not go down due to crankcase vac alone.

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I'm not arguing with this at all.......just learning......
So the "reading" on the oil pressure gauge goes down when crank case pressure turns to a Vac.........Does that mean, that if you had high crank case pressure.....say in a boosted situation, with bad rings blowing into the crank case(no vac system installed). That the oil pressure gauge would read higher at that moment?

When the pressure gauge goes down under crank case vac.......how much does the gauge read...less.......a pound? 10? More???