There are many advantages to playing AAU sanctioned events.
First, it affords team the opportunity to qualify for their resepective state and national tournaments.
If a team plays in its age-group substate and qualifies for the state tournament, there is no additional entry fee for the state tournament. Even if a team does not qualify for the Division I national tournament, it is automatically eligible to enter the Division II nationals.
As a point of correction, birth certificates are no longer required since AAU has gone to a grade format. The main component of the necessary documentation is simply a grade card or report from each student's respective school veriftying he is the proper grade. This ensures that players are playing in the approprate grade group, as opposed to many tournmenents where age groups will be combined or there are no eligibility requirements.
Many teams in Tennessee choose to play in multiple local tournaments that are non-sanctioned while avoiding AAU events completely. This is unfortunate, because I believe we've forgotten the importance of competing.
I think the non-sanctioned events can serve many teams well as tune up tournaments and can provide game experience. However, the AAU sanctioned events follow TSSAA rules completely and utilize high school and college officials. This is not always the case with non-sanctioned events, and in those tournaments you may run into running clocks, non-licensed officials, etc.
While some of these events are high-quality, not all meet that standard.