It is a waiver of liability, it is good practice to have everyone that you work with to sign one. Contrary to what many people believe, they do carry some weight in the court system, PROVIDED THAT YOU WERE NOT NEGLIGENT. It is also necessary to carry personel liability insurence for your self. One million dollars per incident is recommended, it should only cost a few hundred dollars a year and it is worth it. To be a sucessful trainer you must sell yourself and your clients need to see results. You must have a 100% program that covers diet as well as exercise and you must adress lifestyle as well i.e. if a client is going out for pizza and beer every night the program won't work. Clients that are not compliant, suck to work with.