I have used it from time to time. It is a ‘contract’ between the client and the trainer where the client makes a ‘pledge’ to hold up his end of the bargain and ‘do as told’ so that those lofty goals can actually turn into reality. The trainer in turn pledges to give advice to the best of his abilities.
It works very well for some people and truly helps them achieve their goals. It helps the trainer with those who just ‘talk the talk’ but not ‘walk the walk’ and then try to blame everybody outside of themselves if things are not going as they want.
But be careful who you pick for it. Some people will use it to stay stuck in their belief that they cannot do anything right.