It's sending inputs that makes preventing cheating easier.
Some genres of games (like RTS) typically do send inputs instead of state. Cheating is indeed possible.
Cheating in the sense of breaking fog of war, because the client has to actually have the whole game state in memory due to deterministic synchronization. Yes.
Huh? If the server trusts the client to send state then the client could potentially send invalid or unfair state. If the client merely sends inputs then it can't just decide to manipulate the state that way.
He means the server sends state to the clients, rather than sending other clients' inputs (or just P2P if no server). There are games that send inputs, which means if it's a game of limited information, clients know more than they should.
Ah, I get it now. I actually know a game that sends inputs (I commented elsewhere in the thread, the game is Cosmoteer). But yes, most games I'm aware of send state.