High volume vs. high pressure oil pump

Maybe I should have searched before I asked! I know why he used high volume, I was more or less wondering why he was against a high pressure pump and what were the circumstances that would require high pressure? I remember the first time we had this conversation was when I had put my 426 Hemi into a 1966 Belvedere 4 door to street race and after it warmed up the oil pressure gauge at an idle would drop below 10 pounds. Kind of freaked me out because after all I had paid $600 for that Hemi ( kind of like spending $20,000 in today's dollars) and thought maybe I had got screwed when I bought it. Of course the common sense answer was it needs more pressure so when I went to the parts store they ask HV or HP? And I said HP. After he saw what I bought he told me two things I have always lived by, never use a high pressure oil pump and never use Valvoline motor oil, and I never have. So I'm guessing the high pressure pump would only get used on something really loose like those old qualifying motors that Harry Hyde used to use in NASCAR. The reason the question came now is because I just got a 4 inch stroke Magnum motor and it came with a mellings HP pump.