Again, Niantic is always trying to make this harder and less useful than it was in the past. It's financed by online maps with ads and donation buttons, and by people who buy accounts online. With an army of fake characters and a bunch of scripts, botters travel the PokéScape, collecting as many high level Pokémon as possible. In addition to potentially banning your account, Niantic also slashes out illegitimately obtained Pokémon, so they're useless in battle anyway.
Niantic has a long history of banning players caught spoofing, in Pokémon Go and in Ingress before it.
This can get you access to Raids and Gym, as well as lie to the game about how much you're walking.
For a game based on your real world location, spoofing tells Pokémon Go that you're somewhere you're really not. Spoofing: Some people fake their GPS location.
