Nah, this whole construct is kinda stupid. We have a basic system where once units touch each, they are bound together with the strong nuclear force. Unless you have this magical thing called "hit&run" and then like necrons only making it night fight in their turn, you can manipulate the turn structure and abuse the crap out of it.
The whole, "my assault turn, your assault turn" thing is silly too, where it is magically a thousand times better to win combat in two phases, rather than 1. And of course, hit&run, combat tactics, and other weird special abilities let you manipulate the hell out of that, too.
People pretend there's some tactics to it....tuning you CC unit so it kills the enemy in 2 rounds, challenges, etc, but there's really not, even when performed by the best players it's more random than anything else, and it's all so artificial.
I would really prefer a system similar to warmachine's, where a unit can break off, but there's a fairly hefty penalty for doing so (usually a very nasty back stab).
It's why I was so excited by the leaked beta of 6th.... something to change around the turn order would have been great.