Is this measurement conceptually useful, or is it completely arbitrary? I thought it was an attempt to rigorously define "surrounding terrain" for purposes of m

Is this measurement conceptually useful, or is it completely arbitrary? I thought it was an attempt to rigorously define "surrounding terrain" for purposes of measuring a mountain's height above the surrounding terrain, but if it defines the Challenger Deep as "surrounding" Everest, that's topologically interesting but doesn't seem like a useful way of thinking about geology.