Haven't been around AH very long...some guys were saying you should always use Combat Trim, that it helps you retain E by always having you in trim. What are the downsides to Combat Trim?
In Aces High, at least for those without force-feedback sticks, stick travel equates to pull force in a real plane. Trim (such as up trim) just works like in a real plane by biasing what the netural point of stick pull results in as well as giving you (again for up trim) more up elevator deflection at any given amount of stick pull force.
I don't find any performance advantage to combat trim off as long as I can generate enough stick force to give a stall or blackout (i.e., I don't need more elevator authority). There are some limited cases where you can pull the stick all the way back and not black out or stall, such as in a 109 at high speed as one example. In that case, adding some up trim with the stick full back will allow you to pull more g's than with combat trim on and the stick full back.
Combat trim off would mean that your neutral point isn't changing as your speed changes, thus perhaps giving you some element of feel that some folks might prefer during a fight compared to having combat trim on. Combat trim on, though, is just like contantly retrimming the plane as your speed changes; so it might be that some folks prefer the feel of that.
Me, I fly with it on unless I'm yanking full back and need more elevator authority, then I crank in some up trim temporarily (then back to combat trim).