The extremely large calibers are mainly for hunting and giggle factor.I think it is like buying an impractical hot sports car.They do have legitimate uses in hunting large game like grizzly and cape buffalo.Many lives have been saved with these type weapons.If you live in a wilderness area that has dangerous game it is just common sense.My favorite one is a 45-70 revolver.Huge proven round with tremendous power.They do have a legitimate niche.

BFR 45-70 by Magnum Research - YouTube

For my needs, .50 GI is a novelty round. Kind of cool, don't really need it though. I will admit that it looks like fun.
One of the attractive things is that you can convert your existing Glock or 1911 to it without a lot of drama. Once upon a time my LGS carried the ammo, though I couldn't say these days. One of the employees had one on a 1911. It does make that whole "because they don't make a .46" joke kind of moot.
Since it's a rare beast, if you were to want one, you better be a reloader or wealthy if you want to shoot it often. Even then, .50 cal stuff can get pricey.