It instantly raises all SPECIAL attributes to 9. This perk will not lower attributes which are already at 10.
If you have already collected the Bobblehead for an attribute, before you take this perk and the attribute is below 10, you will be unable to raise it to 10. On the other hand, if you choose this and then find the Bobblehead, the attribute will be raised to 10. If you plan on getting this perk and have the Lucky 8 Ball, be sure to leave it someplace safe until after getting this perk, then put it back in your inventory and you'll have 10 Luck.
If you're planning to get this perk from the moment you start the game, it is advised that you shouldn't get the bobbleheads for the S.P.E.C.I.A.L. stats after you start the game (except for any S.P.E.C.I.A.L. stats that are already at 9).