I'm no expert but as far as i know the advantage of a split bowl is to allow you to bolt on things like wedge, snoops, droops, etc.
Here's a pic of my bowl which is a non split bowl.
http://www.reitanfamily.com/albums/p...0963.sized.jpg
And here is a pic i found of a split bowl
http://i23.ebayimg.com/02/i/01/e1/a6/0a_12_s.JPG
Thats only half of it but you get the idea i think.
I'm sure there are other advantages.