Cleaning your piano can be for simple aesthetics, but the inner workings of your piano need to be cared for just as much.  Dust easily absorbs the humidity from the air and fills gaps in between action components.   Each metal component rusts resulting excess friction between parts and the weakening springs.  Felt cloth is used extensively in piano actions and will become hard and sticky as dust builds up.

A simple cleaning of the action and case of a piano reduces the frequency that components and felt cloth will need to be replaced.