At 450+mph it is useful in a 109 to trim down, as AH's auto trim isn't sufficient enough.
Of course the reverse to pull out of a high speed dive, hammer that K key
.
But other than that this "trim aiming" is as AKAK said, "a gimmick" and that's that.
Regardless, scoring a hit by shooting a 30mm on say a K4 over 300yards is always a gamble, as the 30mm is inaccurate and at 600yards is more dumb luck than anything.
Follow the 109 pilot's 30mm rule; 30mm set to 350yards and shoot at icon 300 or less.
But also the information is not wholly correct to my observation, "trimming does not add extra turning ability", there are some exceptions;
Manually trimming nose up on a P51 at low speed (i.e. on flaps,) improves turnrate, and will help win a TnB fight to an identical P51 using autotrim.
This is because autotrim is designed to get the aircraft to fly flat at level at that certain speed, AcesHigh doesn't use separate trim tabs, but moves the whole elevator surface. Therefore there is less deflection angle with the auto trim on in a P51 at low speed, as it wants to point the nose down to level flight.
I'm pretty bad at explaining things, but;
this has been my Ted Talk.