Personal catchers come in waves. When R.A. Dickey pitched for the New York Mets, Josh Thole had the duty of catching him every fifth day to handle his knuckleball. We’ve seen other notable cases like Eddie Perez working exclusively with Greg Maddux during his career.
In most cases, teams will avoid carrying a personal catcher as it limits the choices a manager can make. However, it may benefit someone like Noah Syndergaard to have a backstop he can work with one-on-one.
Syndergaard was not his usual dominant self for most of 2018.