I don't see anything wrong with using a 'magnum' if that floats your boat.
But there is an undeniable point of diminishing returns. Why would you use a 338 Win mag on small southern whitetails when a .257 Robets would be more than enough for the task?
I'll tell you why. I've got a family to raise which means I don't have the money to buy several rifles and even if I had the money, I don't have the time to practice with several rifles. It's one rifle for everything for me.
I've used my FIL's Ruger M77 MkII in .338WM and liked it. So I chose to buy a Ruger as well and I'd have the .338WM if they made it left-handed. Since they don't, I have a M77 Hawkeye (stainless/laminate) in .300WM. I know that I'll be able to hunt anything I ever have the opportunity to hunt with that rifle.
For now, it's one rifle/one load. Maybe someday when I have time on my hands I'll develop other loads, but for now, I know exactly where my bullet is going to hit.