Traditional publishers produce lots of books, have editorial, and production, and design, and marketing staffs, and big budgets. They can do a lot for writers...make bestsellers out of 'em. If you're a brand name author, that's the way to go.
Most of the time, if a writer can land a book contract at all, the book lands on the publisher's list, might or might not get placed in book stores...and if all those things happen, the book will land on a shelf among thousands of other books.
Someday I'll get there.
But...and it's a big but... Self-publishing (once dubbed by The Big Boys as "Vanity Press"), has come leaps and bounds. You know what the #1 advantage I have right now with my self-published books is?
I still own all the rights. I have 2 Kindle books, and Amazon owns the Kindle platform...but not the books. Lulu is my publisher of record for the paperback and hardcover versions of my books...but only because they own the ISBN. I signed no contract with them, and can yank my books from Lulu with a few day's notice. It's a big advantage, especially because as Vice-President of Marketing (in addition to doing everything else for my mythical company I call Sexton Enterprises), I plan to publish Sexton books in every available format I can figure out how to use.
Still... I make no bones about it, I'd rather be published by someone else than published by--you know--me.
...Now that's vanity!