I think the main purpose is to learn how. Kind of like taking a fine arts class and learning how to paint a portrait.
Practically there could be any number of uses for a realistic human. The scenes in the Matrix with the multiple Neos. A stunt where you don’t have or want to use a stuntman. Back filling a missing scene when an actor isn’t available anymore. Making a young Harrison Ford or an older version of a young actor.
In video games graphics power is getting awfully close to being able to render realistic characters like this, though I’m sure there are optimization steps one would need to take before simply feeding something to Unreal or your game engine of choice.
On an individual level if you have a good human portrait, presented well, that’s a pretty nice thing to have on one’s demo reel.
Edit: I’m pretty sure the graphics power is there in modern consoles/PCs. It’s up to the game’s development and graphics team to make the animations look good.
