NEBS contests (Tailgate, Classic, and Kid's Q) require sanctioning by NEBS to make them official events so competitors can accumulate points for the Team of the Year
Other types of contests (Amateur, KCBS) do not require NEBS sanctioning (unless combined with a NEBS contest at the same event) but can be listed by NEBS to help promote the event.
Whether you are sanctioning or listing an event, the process and costs are the same, with one exception. Sanctioned contests require a Cook's Packet to be reviewed and approved by NEBS. Listed contests don't require a Cook's Packet, but organizers are encouraged to submit one anyway, as the review process can often catch errors or suggest areas in which team communication can be improved.
There are three levels of sanctioning, each with an increased number of services and publicity associated with them: