With the Action Boy / Action Girl perk, you gain an additional 25 Action Points to use in V.A.T.S. This is sometimes used as a substitute for a high Agility rating, and is helpful for characters who rely on V.A.T.S rather than real time combat.
With the Action Boy / Action Girl perk, you gain an additional 15 action points to use in V.A.T.S. mode. Compared to the Fallout 3 version of this perk, it awards 10 action points less per rank, but two ranks exist instead of one.
In J.E. Sawyer's Fallout Role-Playing Game the perk would have allowed you to perform two skill-related actions during the action phase, but the results of the skill checks would have always been halved for both.