Boeing Flight Operations Review 737-22
An airplane in steady cruising flight may require some degree of
lateral and/or directional trim inputs to minimize drag. The
trim requirement can arise from improper rigging of flight
controls after maintenance, internal load distribution, fuel
unbalance, and engine thrust setting imbalance. The degree of
trim inputs required will depend on two basic factors: 1) The
degree of controls misrig, lateral unbalance, etc., and 2) Trim
technique employed