I can see why one might blindly call qsort on already sorted data (when using user input), but why sorted data with one out of place element? Presumably that element has been appended to a sorted array, so you would place it properly in linear time using insertion and not call a sort function at all. Why does such a pattern arise in practice?
You would be surprised how often people just use a (repeatedly) sorted vector in spite of a proper data structure or proper insertion calls. It's a lot simpler to just append and sort again. Or the appending happens somewhere else in the code entirely.
As a real-world example, consider a sprite list in a game engine. Yes, you could keep it properly sorted as you add/remove sprites, but it's a lot simpler to just append/delete sprites throughout the code, and just sort it a single time each frame, even if it only adds a single sprite.
So yes, technically this pattern is not needed if everyone always recognized and used the optimal data structure and algorithm at the right time. But that doesn't happen, and it isn't always the simplest solution for the programmer.
