“Any time you sleep, you remove all of your Rads in addition to regaining all of your Health. (In Hardcore Mode, you still don't regain Health, but you lose 100 Rads.)”— In-game description
Upon sleeping, the perk removes all Rads in addition to restoring all health. In hardcore mode, it merely removes 100 Rads.
This perk can be seen as an alternative to Rad Absorption, provided a bed is found.