You are stuck out of position away from the table on your forehand side of the table. Your opponent quick hits the ball to your wide backhand, and you can't possibly get to it and make an effective backhand drive. What do you do? You could reach out and "fish" the ball back with a light topspin, but that allows your opponent to smash or loop kill. Instead, this might be the perfect time to chop the ball. Not only is it easier to do this shot from out of position than a more aggressive backhand drive, but it's a good change-up. However, many players don't use this shot because they don't think of themselves as choppers. You don't have to be a chopper to be able to throw in a good chop now and then. Just remember three principles, and your backhand chop will start to rescue you out of what was before an impossible position.
First, let the ball drop to table level or below. Second, contact the ball more toward the back of the ball, not the bottom, with your racket facing more forward, not so much up, and graze the ball with a mostly downward stroke. Many players chop too much under the ball, and so pop it up. (Top choppers can do this, but that's a more advanced technique involving letting the ball drop even more, and vigorously chopping the ball with a very fine grazing motion. You can learn to do this as you get better chopping.) Third, most topspin-style players tend to chop off the end since they aren't used to the way a backspin ball floats long. So try chopping so the ball hits your side of the table – and watch it float to the other side!