Trimming allows the pilot to fine-tune a flight condition so that it can be maintained in hands-off flight. That gives the passengers a nice ride and relieves the pilot’s workload. The magic of pitch trim is that once your trainer has been trimmed, your airspeed will not change until you reconfigure.
It’s about touch. The trim-savvy pilot waits until the aircraft has stabilized in the desired flight condition—let’s say leveled off in cruise at 100 knots after a climb—before trimming. The skillful trimmer doesn’t fiddle with trim controls whenever a pitch disturbance upsets things. Rather, the pilot allows the aircraft’s inherent stability to restore the trimmed condition. This design characteristic lets the pilot turn to other duties, helping to avoid overcontrolling as well as pilot fatigue.