While is super easy to go on google/smashwords and just upload your book, i still think small presses should get a small amount of thought. The advantages of having a press behind your book varied depending on the specific book, but thay all can get more exposure for you. Some even do editing, covers and website building and so on! Some presses have connections in a lot of different associations and journals as well as retail store contacts. The down side of this is that they earn commissions on your sales or even the rights to your book in some cases....which might not be what you want.
If you decided to go with a press be sure to do a lot of research when choosing the perfect one. If you dont want to use a press, do some research in book associations and journals yourself. Just imagine if your book was featured in a journal with 20,000 readers.. :D
Here's is the most useful website i could find: LitLine
It has a lot of resources for authors!