One-Piece® doors cantilever out from your building, exerting additional forces on building header when in the open position. A One-Piece® door hangs out twice as far from the building as a bifold.
It's like a large airplane wing, the longer or further a doorframe sticks out away from the building at a 90° position, the more torque / stresses it adds to the building header. The building header must be prepared to support the forces of your door in all positions.
Bifold doors fold in half when in the open position, creating minimum forces to your buildings endwall.