There are clear advantages to this route:
- Allowing a lot of control to the writer.
- If you are a person who likes marketing or finds this comes naturally, then you will have a clear advantage. At least you KNOW you have to do the hard work whereas when people get a deal with a publisher they often have unrealistic expectations of the marketing expertise/resources which will be directed at their book.
On the other hand:
- I find the editing/cover art help that my publisher supplies, invaluable. This does not cost me.
- Credibility - this is a fast-changing factor but, for instance, because Edith Horton is not self-published I was able to join the Crime Writers Association - a long held dream and something I'm loving.
Proof-reading & editing (at the danger of repeating myself, here). If writing is a craft, this learning curve, painful as it can be, improves the writer's work beyond measure. I don't think anyone is truly objective when it comes to his/her work.
If you are self-publishing my one piece of advice would be to please, please get your work professionally read/proof-read/edited.