Paul Chek on kettlebells...

To begin with, kettlebell training systems in general are highly functional. Functional exercises are one which improve a person’s ability to cope with the demands of their work or sports environment. The functionality of any exercise can be rated based on its biomotor richness. “Biomotor” means “life movement” and so biomotor abilities are those abilities that are necessary for functional human movement in any environment where you must maintain your own center of gravity over your own base of support. In short, any environment where you have to support a load, without external support, while standing on your own feet.
CHEK.