HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

and what is this for?

The player should be able to keep track of the turn order themselves. This skill is directly related to the player's skill. Even with 14 identical stacks (e.g., single skeletons), it is very important to be able to understand or remember who goes next, especially when everyone is fighting in a chaotic melee.