It doesn't hurt to get some miles on the big boomers on ordinary game before taking it on what might be a once in a lifetime buffalo hunt. That doesn't work out for me very well because a .458 just isn't much of a prairie gun. For someone who hunted deer, moose and bear in the bush it would work. No doubt some genius will find fault saying that some greenhorn thinks he needs a .458 to kill a deer, but if you don't there will be someone else who is critical about the greenhorn who showed up with a "new rifle". Never mind that the "new" rifle probably has more rounds through it than the guide has ever seen.
The point, if any, is that a hunter may have his own reasons for using what he uses. Those reasons may have nothing to do with being best, or appropriate, or versatile. It could just be that he wants to.
Theres thousands of elephant guns sold for every elephant hunt taken. Its a pretty safe bet that most of them are being used for something else. Most are just range toys.