Sort Order is used to organize your sections, rows and seats or your event spaces in the way which you would like them to appear in the list. 
It makes more sense, for example to have row A before row B and seat 1 before seat 2; but perhaps you would like your aisle seats to always show first, meaning that you start in some cases with a number that is out of sequence.

Watch a Tutorial about Setting Up a Venue with Sections, Rows and Seats:
(you will need flash and speakers/a headset)