I wouldn't get too dependent on it, you should be teaching yourself to ride with your legs and your seat. It's great to have both hands free.
If I'm riding a horse that neck reins, I'll have a tendency to rest my hand on the horn or pommel, just because I have no where else to put it LOL. I never really was a horn-grabber, even if I'm starting one. I do grab the horn around barrels, because that is how I was taught. I just never really thought about NOT grabbing it, LOL even though I don't need to.
I do see alot of riders grab the horn when they're in two point at the gallop, I suppose because they can't balance over the horse's neck. Some riders probably just use it as a safety net- just in case.
I wouldn't stress about it, its not BAD.
Every great dream begins with a dreamer. Always remember, you have within you the strength, the patience, and the passion to reach for the stars to change the world. ~Harriet Tubman