Incorporation is necessary when you want to keep things (rules & regulations, policies & procedures, etc.) the same through the entire body.  I don't remember which forum I read it on, but somewhere on this board, someone asked how other groups kept things uniform within the sorority/fraternity.  Incorporation helps with this.
------------------
Kelli
12-DN-94
SSU c/o 1997
something we all should see: 
http://www.seestudio.com/psa.html