Originally Posted by
Loren Pechtel
They have some value. A thief looking through baggage doesn't really want to make it obvious that he's been there, he's not going to go slashing a whole bunch of bags looking for something to steal.
Readers at a security blog I read have already pointed out an easy trick for opening via the zipper, even if locked, and then reclosing. There are demonstrations on Youtube.
I do agree that they serve a very small security purpose, because sometimes the small amount of extra time, or the obviousness that it's being done, is enough to be a deterrent. But mostly they keep your bag from unzipping by accident.