I'll be honest in that I have flip-flopped on this idea myself.
For a number of years, I hunted everything I could (western big-game) with the 300 Win Mag. At different points in my history, I either had one "do all" bullet - which was for years, the 200 gr Sierra Game King. This applies the "KISS" mentality, and makes for an always ready to hunt package, regardless of the game that I was after.
Then, I had the idea to hunt deer with 180 gr/class bullets and switch back to the 200's for Elk. The reason was simple - "Well, I'm a shooter, and I really should have a custom/specific load for the exact animal that I am hunting, lest those animals and other hunters don't think I'm serious about this."
While this methodology does work, it requires the additional sighting in/range time/multiple data sets etc. associated with having 2 (or more) different loads. This load changeout doesn't bother me because I genuinely enjoy shooting and administrative range time as much as anything else, so I don't mind the extra work.
At some point though, the older, wiser man in me figured that I can get all of the range time that I want without having to justify it with needing to switch loads for the sake of switching loads.
The great thing about hunting and shooting, is that you have the freedom to experiment - and to do what you want, even if for no other reason than that you want to do so.
The other great thing is that a deer doesn't notice if it was killed by a 200 gr bullet, nor the elk that is killed by the 150.