- Block level of 50
Elemental Protection is a great asset when fighting dragons, giving Dunmer immense resistance to fire and Nords an immense resistance to frost that can make a dragon's breath attacks almost harmless. A single elemental resistance item of armor can make other races without a base elemental resistance incredibly hardy against it as well.
Needless to say, the benefit of having a shield is invaluable when fighting elemental mages as well. However, having the shield raised when approaching a mage may not be as effective as simply charging at them without other block perks.
If the Dragonborn is equipped with enchanted apparel that reduces fire, frost and shock damage by 50%, blocking with a shield will potentially make you immune to all Destruction spells, since the enchanted apparel reduces the damage in half, and the Elemental Protection perk blocks the other half. However, elemental resistances can never be higher than 85%.
Combining this perk along with the Spellbreaker shield renders not only almost all destruction magic useless, but dragon breath attacks useless as well. Spellbreaker adds a 50 magic protection ward whenever shielding is active.