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

I know that, I'm talking about why they removed the option in the game itself? It was convenient, you just checked a box and that was it, but now you have to search for a line in the ini file and... well, you get the idea.

You had to remember to check this box every time you created a game or loaded a save. And if an opponent is creating the game, you have to not only remember but also have time to do it. Now, it's enough to go into the ini file once and enable it permanently, which is much more convenient.