Many people wrap their bags in luggage using the professional services at airports because they want to know if their bags have been tampered with. But there's an even better use for them, and that is avoiding extra check-in luggage charges.
Airlines are cutting corners wherever possible these days, and one of those ways is lowering the amount of allowable check-in bags. Whereas it used to be quite normal to just expect two check-ins as a given on an international flight, that's not guaranteed anymore. That cheap flight you booked, saving yourself a few hundred, might only allow one check-in. Extra bags after booking the ticket might be around $150, or as much as $250 if you do it at the check-in counter.
That's where the plastic wrapping comes in. If your bags are small enough, take them over to the wrapping station, and for about $15, it'll turn two bags into one. You're not breaking any rules by doing it, and sometimes the check-in attendants will even recommend it. If one of your bags has an extendable handle and wheels, they can even wrap it so you can wheel around both bags on the one set of wheels. Bonus!
I recently saw off a friend at the airport who thought she was allowed three check-ins, only to find out her ticket allowed one. Combining two bags into one meant she only had to pay one extra bag fee, instead of a massive double fee that would have wiped out her travel money in one hit.
Look for a machine like this:
Of course, it pays to be mindful of your ticket and how many bags are allowable when you book. But if you get caught off guard at the airport, keep in mind this trick as a potential saver. If you know it's going to be a problem, make sure your extra bags are small enough. A smaller duffel and a small piece of wheeled luggage combine nicely.