When the Pittsburgh Steelers converted to the 3-4 defense in the early 80s, it was a move made in large part to reflect the shifting nature of the roster, following the retirement of Joe Greene and the depletion of the Steel Curtain.
But the shift in scheme, particularly in time, showed itself to possess valuable rewards, both on and off the field. Chief among them was the scarcity of the formation, which applied equally to roster building and to game planning.
At that time, nearly every team employed some form of the 4-3 defense, which is what opposing offensive coordinators had become used to in planning against.