Armor penetration makes having over 800 armor rating useful; some enemies will have very high levels of armor penetration
Some effects lower damage multiplicatively with armor rating. For example, the Tower Stone birthsign lowers incoming damage by an additional 25% when standing or walking.
Light armors
Caster armors (low weight, lower armor rating, beneficial for mages)
Traditional light armors
Medium armors (heavier light armors)
Heavy armors
Caster armors (low weight, lower armor rating, beneficial for mages)
Traditional heavy armors
Incoming ranged damage is reduced by 15% when using 4 pieces of heavy armor
Overall, armors tend to weigh more.
All armors have “traits” that can be unlocked with the first evasion or heavy armor perk. For every piece of armor of a specific type worn, the bonus is multiplied by the numbers of pieces worn. (see Traits page)
The various dragon priest masks can be changed to light armor or heavy armor variants to benefit from the respective perks. To do this, go to the sanctuary in Labyrinthian where you can obtain the Konahrik mask. When placing the masks on the altar, you can choose clothing, light armor, or heavy armor to swap them.
The light armor and heavy armor variants have additional armor, while the initial clothing variants have 0.