More on AH combat trim. The Fugitive did a good job describing the need for trim, but let's go more into "combat trim" in AH.
Combat trim as The Fugitive said is an automatic function that will help remove the need for stick input to keep the plane headed the desired direction. For example if you were to slow way down (150 for example), then turn off combat trim and accelerate, you would find that you would need to push the stick forward to keep from climbing (I think it's climbing), due to the increased lift on the wings and other control surfaces. Combat trim is smart enough to see your speed and adjust to the correct pitch setting for the speed you are now traveling.
Here is the rub, when speeds change quickly, it's slow to compensate, and when flaps are out, it seems like it gets stupid and over corrects. It seems to over correct the worst, at the top of a nose high stall. For this reason, I turn it off when things start to get slow, during stall fights, and scissors. In a hog for example, I like to set the trim to whatever the setting is at 200 mph. That seems to give me good performance, not a lot of stick force to compensate for things, and is very stable nose high.
