Block filter bypass valve

[VintageMusclecar]

Pros: 100% filtered oil all the time

Cons: If for ANY reason the filter fails or gets plugged, you have NO oil AT ALL.

The relief valve opens on a pressure differential. It only opens when the filter is clogged and becomes a restriction. This is an obvious benefit for those who never bother to change their oil & filter. If you stay on top of oil & filter changes you should never have a problem.

That said, in the event of some sort of fluke filter failure, personally I'd rather have unfiltered oil circulating through the engine than none at all.

I don't block mine, FWIW.