Knobs/lever sets are primarily used in a hall or closet application where a locking device is not desired.

Knobs/lever sets are primarily used on bathroom and bedroom doors where a locking function is required.

Applies to the trim used on both sides of the non-working door of a double door unit, i.e., French doors. 

Trim is used on one side of a non-working door, i.e., Pantry or small closet door.