You have a character that comes from a particular region of the world. The people from this region tend to speak in a particular fashion. It's distinctive, and the moment anyone hears it, they instantly get a sense of the type of environment that the character came from.
It's only natural to want to put that into our writing. We want to immerse our readers into the world. We want them to experience it. Being able to imagine a character's accent is only part of that experience.
However, building accent into the written form is not a simple matter of slapping a few letters onto the page. Like everything else we do in writing, it takes careful thought and consideration.
Writing accent into your story could add the perfect color to your fictional world, but it could also turn into a reader's nightmare.