Free travel is one of the greatest perks of working for the airlines. It’s also one of the most frustrating.

Free travel is great for the obvious reasons: You can fly for free, or nearly so, on dozens of airlines around the world. It’s frustrating because the airlines have become so incredibly good with their capacity discipline that you never can be sure of whether you’ll make it or you won’t.

I’ll give you two recent examples. This summer, one of my kids went to Spain for three weeks. The package included airfare for her. However, my wife wanted to accompany our daughter to Paris, where she would catch a connecting flight to a small city in Spain.

In the meantime, my wife and a friend of hers (whose husband works for the same airline I do) would spend a few days in Paris taking in the sights. For weeks, the flight was looking good. In the last week or so, however, it began to fill up rapidly. The uncertainty lasted until the morning of the departure. My wife and daughter went by the airport early to check in her bag, and the agent at the counter told my wife she should give it a shot. Her friend, who lives in Detroit, started driving.

At the gate that night, the number of standby passengers appeared to exceed the number of available seats. Following our tried-and-true mantra of not leaving the gate until the airplane pushed, my wife (im)patiently waited.

A family of five was unable to get on as a group, and two seats opened up, so off they went. Had she gone strictly by the listings she could see online, she would’ve had to come up with a plan B (there was one in place).

A week after my wife got home, we were scheduled to go on our summer vacation. The trip was to the Cayman Islands, which is one of our favorite places to go scuba diving. Our rule of thumb is to buy tickets whenever we check bags, and we always travel with our own dive gear, which has to be checked. When we booked our trip in the spring, we were tempted to chance using our pass benefits. The flights were wide open, and it would save some money. I sat on it for a few days, and finally decided that the peace of mind was worth it. I took advantage of the discounted tickets that employees can buy, and bought seats.

On the day of our trip, the first flight in the morning took a mechanical delay that would eventually exceed four hours. Some of those passengers spilled over to our flight, and the airplane was full on the first leg. The second leg, which had been pretty promising, sold out during our layover, which means that even if we had started the night before, we wouldn’t have made it.

It was dumb luck that we didn’t get burned by the late departure of the first flight. We considered buying seats on that one, but we didn’t since the layover would have been so long. That flight wound up touching down just as ours was leaving. It would have cost us a full day of our trip.

So, there you have it: two international flights, two different methods of travel. One was pure fun (had my wife not made the Paris flight, she and her friend were going to go to Scotland, which was wide open), and the schedule was a non-issue. The second one, with considerable money invested up front for the resort and diving package, spoke for itself with respect to the logic of buying a ticket. The peace of mind was money in the bank, as was knowing that the airline would take care of us in the event of a disruption to our itinerary.

Not everyone is willing to spend the money on tickets, and not everyone is willing to risk the wrath of the non-rev gods. As the song says, you have to know when to hold them, and when to fold them.—Chip Wright