Trimming elevator all the way up (IE:Elevators making you go 'up') will help
you return to level flight (or avoid the ground) during compression in a dive,
provided you have enough altitutde.
This is kind of true, but not for the reasons most believe.
In a high-speed dive, the CT is actually going to trim your elevators full
down. The problem when you try to pull out is that even when you fully deflect the stick, you're still fighting all that down trim, so you're not getting full up deflection. It's a perfect example of a situation where CT is fighting
you, and where you'd be better off with manual trim...
As soon as you start feeding in up trim, you'll start pulling out of your dive. But you'll be out of your dive before you even reach "neutral" trim, let alone "full up" trim (for the most part). Going to full-up trim would be equally as bad in most situations as full-down, even though it kept you alive momentarily. In this example, once you've pulled out of your dive you'll probably want to zoom climb or extend, and you'll need to fight that full-up trim to do so...
The point of manually trimming is to minimize the amount of fighting the plane you need to do, so you can put that effort into fighting your opponents.