If I'm buying a ticket, I'd rather it be on a full flight where I'm glad I bought the ticket than an empty one where I could have stood by! I spent $440 on 2 round trip tickets DEN-MCO with an employee discount recently. While that wasn't too bad, the plane was wide open, with dozens of seats available by the time we took off. The peace of mind was great, and the fare wasn't *that* bad, but you can't beat free!