Jokes aside, there are some Korean MMOs that rely on excessively trusting the client as a core part of their business model. If you offload as much state as possible to the client your server costs go way down. Maplestory is an example of this: if a player is alone on a map, essentially all map state, physics, etc. is handled purely on the client. When another player enters the map, half of the NPCs get 'handed over' to that player, and the server syncs state between the two clients.

On the other hand, you have to keep in mind hacks like bots and wallhacks. In the case of bots obfuscation is practically your only defense. In the case of wallhacks you can try to keep clients in the dark as much as possible, but there will always be a period where the client knows more than the player should (unless you want enemy players to 'pop in' once they are fully in view).

It also makes the game much more fluid without adding a lot of complexity to hide the latency. I think South Korean games can get away with it because they require an SSN to register. If you get caught cheating then making a new account isn't easy.