Built-in autosave feature (for the TE version).

BUT... While playing as Fortress in The Restoration of Erathia, I reached level 111 and easily captured the maximum number of Dwarves, chasing the poor creatures around the battlefield for about 40 rounds!!! This is definitely more like nonsense...

It's not nonsense, but rather an exchange of resources for time. That's why chess clocks are useful.

Similarly, you can capture the maximum number of Dwarves on level 111 as Dungeon – upgrade the Harpies and chase the Dwarves for who knows how many rounds until you eliminate them all.

I've done it myself; the timer is completely depleted, so it's still unclear whether such battles are profitable.