The fact that you don't have to take actual cash out of your pocket to do it makes it a much simpler/less disruptive thing to do, but the outcome is the same: You commit to work for the employer for a set number of years, and forfeit a sum of money if you renege on the commitment.
This assumes that you are guaranteed a promotion/autonomy/responsibility after a few years - how many contracts have promises of career advancement in them (not the "social contract")?
