Or did some developer at Gamefreak simply have too much time on his hands and gave Sableye a useless signature ability? Note that I'm completely aware that stall was actually introduced some time after Sableye
Stall can be used for moves that are intended to strike second. It also can allow the effective use of items that increase stats if hit by super effective move. Of course this can only be used if the Pokemon is bulky enough.
These things are the benefits, but to answer your question, I've never seen this used competitively, and I don't think I ever will see it used competitively. It simply can't compete with other options that fill the same role.
I find the best way to use Stall is a toxic stall while holding a Zoom Lens, as it increases accuracy if it moves after your opponent. As for being competitive, it's not the best idea. Stick with Keen Eye for Sableye.