The clubs section of the customer database was originally designed to store the customers membership number for supplier sponsored clubs like Lilliput and Swarovsky.
There is nothing to stop you creating your own clubs and by simply naming the club ( in the options screen ) and entering a number you "join up" the customer. For instance you might create a Jade club and mail out customers in the club with items of interest or invite them to instore demonstrations, exhibits etc.
You could also develop your own loyalty card system, for example a gold card system for your best customers and offer rewards or discounts etc .JCT allows you to colour code these club members so their names appear in a different colour ( of your choice )