Most airlines have them. It is a gift the Company gives to thier employees. It is a round trip ticket to anywhere that particular airline flies. (Different airlines, different rules)
These will come in handy if the employee is going somewhere and wants to take a friend or someone in thier family that is not included in the free flight umbrella. Take for example, my son worked for SWA, I could get free tickets (standby) directly from SWA but the mother in law couldnt. The employee can give them to anyone.
It is a standby non revenue pass. You are the lowest priority. No guarantees for a flight. Most of the time you will be one of the last to board.
It can be a little nerve racking at times. You need to have a contingency plan if you arent able to get a seat on a return flight.
Advantages: Its free. Ticket cant be sold. Employee will get in trouble. It can be used anytime there is a vacant seat. My dil used one to fly to her grandmother's funeral. She would not have been able to afford a ticket, too expensive last minute. They come in handy when I found a real good last minute timeshare deal.
I tend to be spontaneous, fly by the seat of my pants kind of girl; so I love these passes. Lots of people like and need to have exact plans. Not worth it for them.