On Oblivion
Affects your ability to maneuver and balance, your total Fatigue, and how much damage you can do with Marksman weapons such as bows. Governs the skills of Security, Sneak, and Marksman.
 On Morrowind
Affects your ability to hit and dodge attacks. It also affects how much Fatigue you have. Governs the skills of Sneak, Light Armor, Marksman, and Restoration.