I have a button mapped to toggle CT on and off as well as all the other trims. I use it for general travel but will turn it back off when in fighting mode. I fly the 38 mostly and find that with CT on, with flaps out, getting slower, it tends to want to give me more nose up compensation than I'd like. With flaps off, nose low and getting faster it gives more and more nose down than I'd like too. Also, if you're flying the P-38L it tends to negate the effect of the recovery flap. In general I prefer a slightly nose down trim which gives what is to me a more natural feeling of pulling the nose around in a turn than forcing it back down. YMMV.
On what Fulcrum was saying IIRC some of the LW birds did have trim tabs on the control surfaces but some of them were only adjustable on the ground. I guess they went by the pilot's personal preference and just left it at that.