Self-debarkation is not assigned a waiting area. As soon as the ship is cleared they make a ship wide announcement for those doing this to go to the gangway.
It is beneficial for those who don't have a lot of luggage, who drove to the port and can just leave and get in their car, or those who have early flights and will just grab a taxi or pre-arranged shuttle.
If I had late flights I would not do self-debarkation. You aren't gaining anything other than being on the other side of the Customs neutral zone earlier. Why do the Teaberry shuffle when you can take your time?