Whenever I go to festivals and other events with wristbands I always try and keep my wristband loose so it's easy to take off later. I like keeping them as souvenirs, and cutting them off ruins them, in my opinion. Also, if you happen to buy a three-day pass to a festival and want to let your friend use your pass for a day, you need to be able to get that thing off and on without ripping or cutting it (not that I've ever done that).
Taking a wristband off can be an exercise in seeing how small you can make your hand, and how you can contort it without breaking anything. Hacks World recently posted a video that makes the process a ton easier using just a plastic bag.
To do the trick, stick your hand in a plastic bag like you might get from a grocery store, pulling the rim of the bag under the band of the wristband. Then pull handles of the bag over the top of the wristband and pull it toward your fist, pulling the bag off your hand and taking your wristband along with it.
That sound confusing? Here's a short video showing how it works:
Unfortunately, the trick doesn't work in reverse, so if you are passing that wristband off to a pal, they'd better have a tiny wrist.