It can be used for comedic effect. For instance, if a small Pokemon like Jigglypuff has a really loud stomach growl, it can be a funny contrast to its cute appearance.
A Pokemon's stomach growl can also be a sign of danger. Maybe in a post - apocalyptic Pokemon fanfic, a growl from a starving Pokemon could signal that it's about to attack other Pokemon or humans for food. This adds an element of suspense to the story. Another way is to use it for character development. If a proud Pokemon like Charizard has a stomach growl in front of its friends, it could show vulnerability and a side of it that others haven't seen before.