It grants you another immediate level up. So in essence you lose a perk to get an instant level up with the extra skill points, and a perk aswell.
Example you reached level 10 assign your skill points (varies from 11 - 23) then get the Here and Now Perk. As soon as you click finish, you are at Level 11 and get to assign another set of skill points, and pick another perk.
It basicaly boils down to if you don't mind losing a perk slot for this one time perk use.