The Falcons have been without Sean Weatherspoon for the past three weeks because of an ankle injury. With the lack of depth, the Falcons potentially could have called on Biermann to fill the gaps.
"We only had four active linebackers on our roster," Smith said. "Two injuries would have put us in a position where Kroy Biermann would have had to play linebacker in an emergency situation."
Biermann is playing a hybrid position. He's more of a traditional defensive end in the 4-3 defense. When the Falcons use the 3-4 or 3-3-5 alignments, he's more of an outside linebacker.
"We ask him to rush the passer," Smith said. "We ask him to cover backs. We ask him to cover tight ends. We ask him to close the middle of the field. You just don't know where he's going to be."
Biermann, 27, was a fifth-round pick in the 2008 NFL Draft. In five seasons with Atlanta, Biermann has racked up 95 tackles and 14 1/2 sacks in 74 games. He started 20 of those games.
This season, Biermann has played in 10 games, starting three. He's racked up 21 tackles and two sacks.
The Falcons (9-1) travel to play the Bucs (6-4) on Sunday at 1 p.m.