WHAT IS THE DIFFERENCE?
Certain applications may require a locking slider. Locking sliders are assembled with a small pin that nestles between the teeth on the zipper chain. This locking pin prevents the slider from moving down the zipper chain and opening the zipper, until the slider tab is pulled, thereby retracting the locking pin and enabling the slider to move freely up and down the zipper chain.
Nonlocking sliders are manufactured without a locking pin.
Those applications that would best be served using a locking pin are trousers, pant legs, front of jackets and other applications where you need the slider to "stay put" and not move unintentionally.
Nonlocking sliders are best used on those applications where there is no (or very minimal) crosswise tension against the zipper chain.