Plugging cam tower oil holes question.

I am wondering what is the reason for doing this? I know everyone does it and all but what is the exact purpose for it?

i not sure what you are saying in pluging the holes a lot of people weld a plate to the top of the towers for strength because the thin tops are the weakest point to the heads

I believe that some cam bearings are grooved on the non bearing side (makes installation easier, no oiling holes to line up). So if the hole on top of #2 and #3 aren't plugged, then a loss of oil pressure will result.