Which Granite (http://tanbrown.org) s should be sealed?

I have St. Cecelia in 2 bathrooms, Sienna Bordeaux in the kitchen and (http://maplered.com) master (and (http://maplered.com) as a filler in the fireplace), Uba Tuba in the utility room and (http://maplered.com) two kids bathrooms, and (http://maplered.com) an unknown black Granite (http://tanbrown.org) in another bathroom (I'm pretty sure it was a builder grade because it was a remnant, if that helps). Should all of them be sealed? And once sealed, how often re-sealed? Thanks for your help.