It exists because of machining, but it MUST be removed to clean the galleys out properly. Anything that plugs a passage leaves a low volocity spot next to it. So debris will fall out of the oil stream and settle there. I've found several blockis that had two plugs, one on top of the other. But it must be installed to keep the oil flowing where it needs to go, as opposed to the path of least resistance. And every plug MUST be removed, and every passage must be brushed clean.