Word bubbles, they can add a lot to a panel! Just like anything else in comics, they can add a lot of life into the story if you have a little fun with them! I like to use them to express different ways in which the characters speak, or feel, or how they interact with each other.
For example, if a word bubble from character A is closely followed by another from character B (or outright covered by it), it can translate to character B replying quickly to character A, or cutting them short in their speech, you know?
Comics are fun :)
*This is a rerun of the finished webcomic Go Get a Roomie! You can find these two strips in the old archive >here<!