Publications can be a great way to organize your writing. You could have one publication for Humor, one for Fiction, one for Essays, one for Poetry, etc.
Or for genres: sci-fi, romance, adventure, etc.
Which makes them also useful as portfolios, as you stated.
They can also be good for publishing a novel in parts, to keep it organized and easy to find.
But once you open publications up to other writers, they become a whole different animal and a lot more work.