The catcher has to know where the ball is going to try and catch it. Passed ball could result in base runners advancing or scoring.
It’s the catcher’s responsibility (perhaps in collaboration with coaching staff on the bench) to relay the pitch type and location.
Catchers use finger signs, touching shoulders or arms etc to signal which pitch type, and usually glove position to indicate a target. If the opposition “cracks the code” and can signal the batter, he will know where the ball is going and can effectively hit it or know to lay off if it’s not going to the strike zone.
Google “Houston Astros cheating scandal.” The Astros effectively cheated their way to a World Series championship using cameras and banging on trash cans to signal hitters.
