The more throws you are able to throw the better because you will be more of a threat to your opponents and the harder they will have to work to cover all of your players when you have the disc. By having the hammer as an option, you will be a huge asset to your team and you will force the defense to be more aware when you have the disc.
You will hear many different things from many different people, but there are several cases in which I think a hammer is useful: