The thing that most stood out to me about balance factoring into gameplay was being knocked back as opposed to being knocked down by things like Minotaur charges. With high enough balance you'll be pushed back but remain on your feet and not knocked prone. (While I haven't specifically looked at it, my guess would be this is the same for things like air elemental knockdowns; the higher the balance the less likely you'll end up knocked down as opposed to just being knocked back.)
Having said that, not all knockdowns are the same. The Forgewraith Titan in Too Hot Too Handle does a slam that apparently knocks you down no matter how good your balance skill is. The time it takes to get up from the slam seems to also be the same for everyone hit by it regardless of their balance skill.
Armor Check Penalty is supposed to also factor into your balance skill. The higher your ACP is, the bigger penalty you'll take on your balance. This is more so an issue when wearing heavy armor as opposed to something like cloth or light armor, but the ACP can be reduced by various enhancements and augments.