The 320 is the only aircraft where I have seen the SOPs have the radar 'as required'. Persoanlly, I don't like it - for the reasons discussed. I have seen people fly towards large clouds with the comment "There's nothing in there", to which my answer is usually "How do you know? The radar's off!".
I can see the maintenance arguement. But on the other hand, I've heard that switching it off in flight with the avionics cooling in full flow can cool the magnetron too quickly which shortens it's life.
And leaving it on in areas with 'military tension' is a very good idea. The military aircraft I used to fly had a Radar Warning Receiver which would identify a radar as a civilian weather radar. It might just just prevent you getting a rocket up your @rse!