What are the three power modes on the SV12 and when should I use each one?

The three power modes are Eco, Auto/Med, and Boost. Eco mode provides maximum run time for longer cleans, Auto/Med mode provides the optimum balance of power and run time with suction automatically adapting to dust levels when a cleaner head is attached, and Boost mode is designed for intensive spot cleaning of ground-in dirt. (Page 3)