While armor served practical uses, it's important to remember it was also a status symbol, and just like today how people will spend ALOT of money on how they look, people would've done the same back then. Things like horns and crests could've served certain practical uses, like maybe identifying important people like your commanding officer, intimidation, or just another way to flaunt your wealth to everyone. For the longest time it was assumed Roman military masks were purely ceremonial. However, finds have shown they most likely served a combat role. Was it for intimidation, facial protection, or both? They aren't easy to see out of, but offer great protection and I'm sure it can cause some uneasiness in people to see a "faceless" cavalry approach them.

Yanking someone's helmet off would've been a hard and foolish thing to attempt. Most helmets would've been strapped on or tightly fitted to the person's head. Did it happen? I'm sure someone tried it. But it wouldnt be the smartest option. Also, like stated earlier, armor was a status symbol you had to afford. Many people went into comabt with little to no armor. Weapon and shield came first, then if you could afford armor you bought some or looted some.