The horn is basically a tool for working cows, to steady yourself when cutting cattle, barrel racers hold onto tall thin horns when turning barrels, etc.
Trail riders hang stuff on it. ;)
Greenhorns hang onto it for dear life. BTDT lol The mane is a better anchor, especially for going UP hills. I don't advise holding the horn steep hills.
You can push against it to get your butt down when needed, or grab the cantle and pull your butt down. *til you get your seat anyway.
Dallying your mecate line if you don't want it in your belt.
Lots of uses, just not supposed to use it for balance under normal riding conditions.