Yes auto trim is really useful.
What Sorrow says is absolutely correct. The planes in this FM have a lot of rudder authority, and even the slightest slip angle (ball not centered) can result in a lot of drag.
I have all the manual trims and two of the auto trims (level and angle) mapped on my HOTAS.
My favorite application is in a dive.
If I will be in a long dive to attack a fighter or ground target, I will push my plane into the dive, then select auto-angle-trim. This will trim the plane for this dive angle, and you will have a nice, well-trimmed shooting platform.
Be very careful at the end of the dive. Because your elevator is trimmed to hold the plane in a dive, and because the increased dynamic pressure at high speed will limit your elevator deflection, you will need some "up elevator" trim in order to make a high-G pullout.