[eluser]tonanbarbarian[/eluser]
class variables, or properties as they are called, can be useful for lots of things
for example I store any validation rules for a model in properties of the model and then retrieve them to set the rules. This allows me to keep all of the information about the model in the most logical place, in the model
I also use it for automation.
I extend the default model and add methods to load, save, delete etc, and having properties that indicate the name of the table and the primary key etc come in useful in this situation.