FPS Weapons, do you need 1st and 3rd person?

As the title says, most tutorials seem to have separate 1st and 3rd person models, as most FPS games do. Is this necessary? Can you make a game using the same model for 1st and 3rd person or do you run into problems this way?

if you have a weapon system that requires 2 meshes, you can set them to reference the same mesh, and it shouldn’t cause any technical problem, it just might not look as good as having a separate first person mesh.

I don’t just mean model wise, but will there be issues from the code standpoint of the game? For instance, if I only have the single model in the game world, would that cause issues?