If it could deduce density from the material name, it'd useful for volume-to-mass conversions., e.g. 1 cup of butter -> g Not sure if it's quite scientific though... :)
I'm trying to think of how you'd specify density of butter, perhaps "butterdensity", cognate, "earthmass".
I've got a number of geographic areas specified, so I can give you, say, paper size in milli manhattanarea.