Hi all,
Yes I teach my students to trim on final approach - I do to - probably down to 200' I will trim...
Why need to trim on final approach? Because
1. You may change the aircraft configuration - u/c or flaps
2. if you alter the throttle one iota you need a trim change
3. approach speed and threshold speed are unlikely to be the same.....if you fly threshold speed on base you are endangering yourself...so a change in airspeed results in a change in trim.
4. if you change the attitude on the final approach its best to trim - if you hold the pitch change in then you are making a lot more work for yourself and the approach will not be as accurate.
Hope this helps.