Why would you keep a device suffering from wear and tear when you have clear skies and thus obviously not required?
low level windshear can occur in clear skies depending on the topography. As commented, some "States" require weather radar to be on when transiting their airspace. There is no evidence that the WX Radar is harmful to crew as it points forward, although the constant grind of the gimble can be annoying. Guess we just stick to SOPs and let other higher powers decide!