It's pretty useful but not terribly. It adds based only on the base rating of the armor, so the highest amount added will be 18 points when wearing Daedric Gauntlets. However, if you add unarmed enchantments you can start doing a lot of damage and actually make unarmed a semi legitimate combat style.
I add it more for the sake of fun than for use. It's nice to get into brawls with the people in taverns who call you a milk drinker and beat them to death with your bare hands instead of stabbing them, but without enchantments and this perk it takes about 20 minutes to do so.