#2
It locks the strings at the nut, and if you have a floyd rose, also at the bridge. It keeps the guitar in perfect tune if the strings are properly stretched.
My Gear:
American Deluxe HSS Strat
Crate GT212
Vintage '66 Fender Champ Amp
Dunlop Crybaby 535Q
Jekyll & Hyde Ultimate Overdrive
Vintage '74 MXR Script Phase 90
Vintage '77 MXR Flanger
Orange Squeezer (clone)