The more work you do yourself, the more money you get to keep. It's a sliding scale.
Full-bore old-school publishers do almost all of the work beyond the writing, and they like to keep most of the money.
Pro: You get to go onto the next writing project, and you get some money (your advance) up front. Once the edits are done, you are no longer particularly responsible for the thing. Note that this may also get you qualified for membership in some writer's societies.
Con: You don't get too many more decisions about this work, and you only get more money if the book REALLY takes off. If you use an agent you have to split the money with the agent (on the plus side, the agent probably got you more money to split!)
Full-bore self publishing means you do ALL the work yourself (all the layout, manufacturing of books, deployment of e-books, marketing, etc, etc), and you get to keep all of the money.
Pro: You get all the money!
Con: You do ALL the work. And it's a LOT of work. 396
Which prevents you from writing the next book just yet. Especially the marketing parts - that's a hard thing, and if you want to make a big splash (adds in newspapers and magazines) it's awfully expensive.
There's relatively few people doing absolutely EVERYTHING themselves, because it's just too much.
Pretty much no one prints their own books (they go to a printer for that). Maintaining your own printing plant is just too darn much overhead.
Lots of folks don't do their own layout (there are people and companies who will lay out your book for reasonable fees). The same companies may be able to do e-book layouts as well.
Few people sell e-books from their own website - Amazon is more than happy to run servers and deliver books to the large variety of devices they support. Apple and B&N have systems for this as well. If you want your e-book to have DRM, you really need one of these guys to have a significant audience.
There are folks who hire free-lance editors to edit their works before publication.
You could hire a marketing firm to try to promote your book, if you've got the cash and you want to.
Publishers are evolving to understand the new market realities, and you can count on seeing lots of companies with new approaches as time goes by. Most of these are going to be more middle-of-the-road sort of deals (especially in the e-book only publishing world), where you do some of the work, they do some of the work and the money is a lot more favorable to you. 396