When I draw cameos, its often either for gags, or I enjoy the series/characters based in it. Sometimes I just do it for sight gags, like visual cameos without dialogue. But if I find a particular thing for them to say, while staying true to their character, I'll put it in.
Cameos don't really get far in my novels, unless its for a proper plot convenience, or to have my characters feel like they're in a bigger world. I've done it a few times before with friends I've known on other sights, but I've yet to fully commit to a cameo featuring any of my friends on Tapas. One day~. There's some good folks I buddied up with here, or just genuinely enjoy that I want to feature in my work, even if its for a chapter or two.