* Traditional is slow...really slow. Even after your book is "done" it may take 12 - 24 months to hit the market (many reasons for this that I won't get into now).
* Traditional opens venues not available to self-publishing (bookstores, more foreign markets, teaching possibilities, awards, movie deals)
* Traditional provides "credibility." Many readers won't buy a self-published book no matter how many good things they've heard. There is still the idea that "If the book is good, why doesn't a real publisher put it out?"
* Traditional offers advances, which can be a big infusion quickly (but for many books this advance might be quite small)
* Traditional provides an entire team to work with you: Marketing, PR, Sales, Editing, Cover Design
* Self publishing gives you higher % of profit - the same book published traditional or self- will more than likely produce a higher income through self.
* Self publishing has complete freedom - you can choose your own release schedule and put books out as often as you can create them (traditional tends to "space out books")
* Self publishing may require you to pay money up front for certain tasks: editing cover design.
The one thing that really doesn't change between the two methods (but is often noted one of the reasons people chose traditional) is marketing. Either way you go the author will need to actively market their books. The publisher will "push" your books for only a very small window (just prior to release) and they have many authors to divide their time among.