Let's say a certain airline I know that was bonding people illegally in a certain EU state, did it purely as a paper exercise. It was completely illegal. If you are in that company for at least a few months the word would have reached you that people still leave, and no one chases them for the money. Effectively it was an illegal practice (is it illegal if it is not enforced?), that was never enforced. A lot of people were still scared to leave regardless, so in a way it did work for that airline. The so called bonding is a piece of paper a person would have been forced to sign at a joining date in a form of IOU. I can't remember the exact wording, but it was very simply written on one side of A4 paper.