To expand on what was already said...Combat trim 'tries' to trim your plane to the effect that if you let go of the stick your plane will not pitch or yaw. The advantage of that is you have a stable gun platform. In a boom and zoom engagment, it is a help to have the nose staying neutral.
In combat, having yaw trimmed neutral is very important. If your yaw trim is not balanced your plane will want to depart to the unbalanced side in a hard turn.
Elevator trim in combat turns is not as important. Since lift and loss of lift happens at the wing, the critical factor is the pitch of the wings in relation to direction of travel. Elevators are merely the tool to change that pitch. Therefore it doesnt matter whether you are gaining pitch with trim, elevator input, or in combination of the two, the lift the wing can provide at a given angle is still the same. I mention this because there is a myth that setting trim tabs max up will make your plane turn tighter, but the limitations on your planes turning ability happens at the wings, not the tail. So my answer to the original question would be, dont bother adjusting elevator trim in 'turn and burn' combat.
One more factor to consider when using combat trim. When you are turning you displace more air, which in turn slows your plane. As you slow combat trim adjust elevator tabs up, which in effect adds elevator input. If you are riding the edge, that extra input may send you over the edge if you are not prepared to compensate for it.