The problem I'm having is looking at a game and I think it's using vertex painting, but not being able to confirm it. I don't want to get it wrong and then I hand it in and someone says "well, actually that's a custom texture." You know? Any concrete examples would be super appreciated!
Crysis 2 I think, and more than likely Crysis 3. Uncharted Golden Abyss as well as Uncharted 3...anything that has a terrain system... I think Skyrim used more decals than vertex painting but I could be wrong. It's been a while since I've been in the game.
If you have large surfaces, such as landscapes or walls etc, you almost always want to use vertex paint to break up the tiling and add things like dirt. If you had to make a unique texture for all those, the texture size will end up being huge, meaning using lot more memory then needed.