Originally Posted by
Paplover
My understanding is that those without seat assignments are at the top of the list in case involuntary denied boarding is needed. But as mentioned DL is very proactive on getting volunteers, in one case paying thousands of dollars to each volunteer. Plus even without a seat if you have status the chances of IDB is effectively zero in the rare case someone does not fly.
Different airlines have different rules for this, which must be published and followed. IIRC DL uses elite status, fare class, etc. before seat assignment and/or check in time.