Another potential benefit to use a RDBMS system as a queue is that it can make it much simpler to express priorities in cases where it's not a simple FIFO, i.e., if the next job a consumer should take depends on more than just the time the job was added to the queue.

One place this has come up for me is when the next job that's picked depends on currently running jobs, e.g., each job is associated with a user, and if a single user already has N tasks running you may want to prioritize another user's tasks for the N+1 slot.