Is it bad to take characters in the background and use them for your story?

I mean those characters that are in the background and come out once or twice in the whole series, comic, manga, movie, etc ... They never have any dialogue or anything, they are only there among the public and nothing else, however their design seems beautiful or attractive, so you want to use it, give it a story, personality, etc.

It's up to you if you want to modify it a little or keep it as is...