I bought an entire exhaust for my bmw years ago. the car doesn't get 5000 a year, if that. i've had it i think 27 years.
i used to start it, let it warm up and turn it off. After a couple years and maybe 2000 miles or less, big hole in the muffler. i called the co, they answered their phone. I told them my story and the guy explained......
that's the worst thing to do to an exhaust, water builds up in the bottom of the muffler and if you don't drive it, the water just sits there.
lesson learned, now i start it and at least drive it up and down hills etc.
Very good point - condensate can build up and typically doesn't dissipate quickly if the exhaust isn't warmed up...
-Chris