Lately, I've started watching glitch channels. "Why", you might ask? Well, at first it was just for fun. But as I kept watching, I started to realize that not all the glitches were fun, pointless, or harmless. What do I mean by that?
Well, watching glitch channels has shown me just how many ways there are to exploit minor oversights and either totally bypass giant chunk of the game, or even bypass the entirety of the game.
I'll admit, finding ways of breaking a game after you've already beat it can be fun and greatly improve replay value to any game you've got, but some of these bugs were serious. Like the backwards long-jump in Super Mario 64, Navi Diving in Legend of Zelda: Ocarina of Time, the infamous Pokemon Blue/Red Missing Number, and Pokemon Silver/Gold Coin Case.
Watching these glitch channels is good for a dev in much the same way a Let's Play with commentary is. I watch Let's Plays to see how gamers interact with the game they're playing, how they think, how they react, where they look when they can't find something, how long they usually go before consulting a walkthrough, what they enjoy doing, and most of all, their comments and suggestions.
I watch glitch videos for much the same reason. To learn what ways gamers break and exploit a game's oversights, flaws, and elements. As a dev, you may find yourself saying "Eh, there's no way in hell they'll find a way to break this. It's so obscure."
Watch A+Start, here, where he spends half an hour abusing the Legend of Zelda: Wind Waker HD remake. Nothing is too obscure. And that's why I'm watching these. They teach me ways of thinking about my programming and level design, in order to avoid some of these bugs and glitches.