In the ggChronicle stream, they often talk about chat bans. And those bans are not in the official banned champions of the game (those at the bottom of the character select screens)
So what are they and what is their use?
They just add one more ban to the game, because they think that the current amount of bans isn't enough. Every team bans one champ while being in the invite room, by chatting. Then the game starts, no team is allowed to pick that champ when it is chat banned, by the rules of the tournament.