Agility has a highly notable influence on your defense. Every point Agility gives +8 points in defense calculation (which means a char with 50 Agility will have 320 Defense rating more then a char with 10 Agility).
Thanks to this a high Agility char will be hit significantly less often then a low Agility char
The bonus is 1% per 1 point of Agility, within a certain range of the stat.
The percentage bonus begins at 25 Agility, and ends at 65 Agility. Examples:
Yang the Barbarian swings a Scimitar, which rolls a strike of 10 damage. He is fully proficient, so he gains 5 base damage, for a total of 15. He has 45 Agility, so his base damage is multiplied by 1.20, a gain of 20%. His final base damage is 18.
Thereafter, he gains 3 points of damage from his personal Bless buff, which gives an additive bonus. His attack lands, attempting to deal 21 damage.
The creature Yang is fighting is 25% resistant to slash damage and is wearing weak armor. That creature receives the 21 damage, which is reduced to 20 by the weak generic armor. That 20 damage is then reduced to 15 by his 25% slash resistance.
Yang deals 15 damage, and shouts with exuberant joy as his target crumples into a heap of loot.