Behaviors are one of the best things that have been added to CakePHP 1.2, they allow you to add functionality to your models in a very elegant and modular fashion. They also promote a lot of code reuse. Perhaps a real life example would illustrate it better.

They show how to create behaviors that can perform a save() call on an image with the backend code doing all the hard work. They create the two methods - dontActAs and nowActsAs - to make attaching and detaching simple.