Why would I choose to Self-Publish my Book?

The biggest single advantage of self-publishing is control. You decide to publish your manuscript and forego the rejection slips coming from cautious publishers. Keeping 100% of your rights–the intellectual property and copyright of your book—may be very valuable. Keeping 100% of your royalties–you can make more money by setting your own retail and wholesale contracts. The personal satisfaction of marketing and meeting your audience to fulfill the purpose of sharing your knowledge and experience of your subject can be significant.

 
For more answers to your questions on self publishing:
http://www.betterselfpublishing.com/