With recent news that the Steelers are in talks with veteran offensive tackle Winston Justice on a free agent contract, it's reasonable to assume the team is not sold on the depth of its offensive line - the tackle position in particular.
Mike Adams and Marcus Gilbert will do battle for the left tackle spot, with the other moving to right tackle. But if Kelvin Beachum is moving inside, as reports have suggested, the team will need a back-up tackle who can play both spots
The team doesn't intend to sign free agent Max Starks to a third consecutive one-year deal (although the door is still open, says, general manager Kevin Colbert), but if they're talking to Justice, they may as well talk to Starks too.
The point is they need depth at that position, and right now, they can rely on Beachum, a second-year player, to learn four positions (both guards, both tackles), or expect depth to be found somewhere in their undrafted free agency class.
Judging by where the team is against the salary cap (approximately $1 million available before the contract of former Steelers OG Willie Colon comes off the books and before the team signs its 9-player draft class), if they're going to make a move, it seems another move is still to come.
However, they could simply enter minicamps and see where certain players are in terms of shape and preparedness, and make a decision based on that.
Whether it would be Justice or Starks, or no one at all, is a matter of some conjecture, but the fact Beachum is currently listed as the back-up at four positions, ostensibly, can't be something they plan to keep in place this season.