>>>>> Volunteering to bump is best if you have no checked bags.

I don't know about that - -I've done it many times, and the advantage is that when you finally get to your destination, you go straight to the baggage office and pick them up, and you are out of the terminal before the baggage carousel even starts cranking up (mind carefully your luggage receipts so you know where they are; I tear them off as soon as I get them, and put them in a regular spot in my wallet).