Basically, locking tuners do not detune easily, as they ,well, they lock. Normal tuners don't have this locking mechanism, which means they can unwind and therefore cause the tuning to go awry. Locking tuners lock the cylindrical part of the tuner in position, so that the strings cannot move, therefore effectively keeping the guitar in tune indefinitely. Most ppl use locking tuners when they have guitars with floating bridges eg. FRs.