Fallout 4's excellent (and informative) video series has reached the letter A in S.P.E.C.I.A.L. These are the defining attributes that will carve out your experience in the wasteland.
Agility lets you work more decicively in VATS. (VATS is what turns Fallout's real-time combat into a stop-time affair.) Also, Agility lets you take a quieter approach to combat encounters, and can turn a sneak attack into a viable tactical approach. But, keep in mind, enemies may have the same idea. It's adorable near the end of this video, watching Vault Boy repeatedly stab a sleeping person in the chest.
Fallout 4 is less than four weeks away. Total atomic annihilation hits Windows, PlayStation 4, and Xbox One on November 10. [Has panic attack, dies.]