I have used buddy passes on two occasions. My feeling is that they are not for the faint of heart nor for travelers not well versed in the ways of the airlines. Their priority is LOWEST on the list, only higher than dirt and dogs (and I am not sure about the dogs). They incur a fee for the airline, do not earn segments or miles, and should only be used by persons who do not have to be somewhere at a particular time.
If there is a good fare sale, it often pays to pay for the ticket, get the segments/miles, and get a CONFIRMED seat.
Buddy passes have their place, I suppose. But, again, if you have to be somewhere at a particular time, do not try to use them.