I believe the bushing is a bit more tolerant to alignment mismatch and input shaft wear. The closer the trans input shaft centerline to the crank centerline, the better for bearing, bushing, and input shaft.
Like most of the clutch components, it only wears while the clutch is disengaged and the motor running. Keep your damm foot of the clutch pedal while driving and don't slip the clutch any more than absolutely necessary.
