...that if you switch from organic to metallic brake pads it is a good idea to also change your rotor?

Pads and a rotors pair when small amounts of pad material are bedded onto the rotor, so an older rotor will not perform optimally with a new pad type because it's bedded to the other pad material.

It's also a good idea to keep an eye on rotor wear in general. SRAM recommends replacing brake rotors when the brake track measures less than 1.55 millimeters thick.

To learn more about these and other brake-related topics, check out Bicycling Magazine's guide to disc brakes.