I'm in the middle of playing the new Infamous: Festival of Blood DLC, which gives series hero Cole McGrath all sorts of new powers by virtue of his getting in turned into a vampire. I talked a bit about the Shadow Swarm flying ability in my hands-on preview and when I was demoing the game, I mentioned that it reminded me of my favourite power in this year's electric superhero sequel was the Lightning Tether. Lightning Tether lets Cole zip around the city of New Marais via electromagnetic tendrils, kind of like Spider-Man's webs.
Upon hearing that, Sucker Punch's Ken Schramm let me in on a secret, which is that Lightning Tether actually started as a bug during the development of Infamous 2. QA testers discovered that there were times when aiming and firing electric bolts at the environment would cause a glitch that yanked Cole forward. QA brought the quirk to the attention to the rest of the development team, who thought it was cool. The Car Lift power in the game came about the same way, as a result of things not working as originally intended.
Schramm point to these two features as part of the advantage of having internal Quality Assurance dept. If QA was handled externally, the glitches that became Lightning Tether and Car Lift would been killed, never to become the cool powers that made it into the game.