Some people are worried that people can still open your locked suitcase,then close it up so you won't notice it has been tampered with. If you secure the zip slider to an anchor point on the suitcase they cannot close it after opening.
This maybe enough of a deterent, so they don't open your suitcase in the first place. Most suitcases have a metal ring up one end of the zipper for this purpose.
Had posted this earlier, but was removed?