Just generally, self-publishing is predominately devoted to the fanzine, with a smudgey wink to memoir & biography and the poetry that no one will publish, no matter how good it is.
For a writer there are greater freedoms; whether to indulge in scatalogical excess or promote an unpopular position or be otherwise indulgent.
In reality, self-publishing across the media can range from terrible to terrific and isn't guaranteed to be narrow in its application. For every artist who wants a forum for drawing bushy eyebrows, there's the cartoonist who needs to take at least part of their work out on its own. And, of course, for the lucky reader who wants to intellectualise there's the possibility of a publication that doesn't chase the bottom line.