One simple example why I do enjoy the engagement rules as they work right now:
Yesterday, I had to deal with a little group of orcs. Nothing major, just a couple of younglings and two warriors or so.
I had all of the minor threats cut down except of one, who had ventured a bit further up north in the beginning for sightseeing purposes, and was now making his way back to watch his two bigger comrades getting hammered by my men. Because I was not looking forward to have my guys being charged in the back by an infuriated orc young while they were pushed around by the two warriors on the front, I sent up a single greatsword in heavy armor to deal with him. The orc was on high ground, but I engaged nevertheless because I did not want to suffer his charge.
This was only possible, because I knew my move would pin him up there, lock him in place by the sheer presence of my guy and keep the pressure off of the rest of my group. With their current equipment, the two orc warriors were more than enough for them.
However, I underestimated the young orc a little bit. I missed the first hit -it happens to the best of us and I don’t blame my guy for that- and in his own turn, he completely tore the heavy armour on my greatsword to shreds and reduced him with a second hit to one, exactly one hitpoint. Suddenly, I was not so fond anymore of keeping him alone up there, all by himself.
If zones of control and disengaging were not much of an issue, this situation would have not been as tense. But it was, and I really enjoyed it. My mind raced and my hand shivered as I gave the next commands, fearing for the life of one of my best soldiers.
The solution was -funnily enough- presented by zones of control again. While most of my guys kept bashing at the last orc warrior (his comrade had fallen by now), I moved a pikeman and a shieldbearer up to my greatsword. The pikeman managed to push the young orc off the hill, the shieldbearer took his place, and my greatsword was free to move away and into safety. He was out of any control zones and the orc was pinned down by my shieldbearer, and thus could not pursue his beloved punching bag.
So instead of simply moving the greatsword away, I had to utilize the abilities I had to get him out of this mess. On the other side, I could use the very same tactic against the orcs to keep them effectively from pursuing that last hitpoint as it limped away.
Moments like this make the battles much more enjoyable (especially in forest fights, which I absolutely love) and therefore I strongly recommend to keep the engagement rules as they are.
Plague Rats - we're not famous, but we get the job done.