Some developers treat their software like a baby when they test it or show it to others. Tapping cleanly and slowly, giving animations time to finish, scrolling slow and smooth, etc.

I like to beat the shit out of my software when testing. Constant erratic scrolling and zooming, multi-touch shenanigans, pressing multiple buttons as fast as I can, using back gestures and the browser back button (if it's a web app), changing the window size and orientation frantically, and just all kinds of rough usage.

If your software can't cope with these things then you're doing a disservice to your users.