NFL teams plan for any number of contingencies on Sundays. It is a physical sport, and all it takes is one play for a player to get injured. An injury to the wrong player can completely change the game plan. Far down on the list of planned contingencies is the backup punter. Not only does that create the need for someone to actually punt the ball, but often the punters serve as the holder on the field-goal unit.
The Steelers unfortunately had this depth tested in Week 1 when P Cameron Johnston went down with a season-ending knee injury.