I let SS cut in round town occasionally in my MiTo JTDm and my Parents 500 TwinAir, but it's switched off when I get on the motorway so that if I hit a traffic jam, the engine doesn't stop straight away after a high speed run, as I always let my cars idle for a couple of minutes before switching off, especially after a long or fast drive. This is to allow the oil circulate round the turbo and cool it down a bit.
Personally I think SS is only there to help lower the claimed CO2 figures and car manufacturers probably care very little if the turbo or another component fails as a result of the SS system. Chances are failures will be after 3 years and it'll then not be them picking up the bill. Plus, if the customer still goes to the main dealers, the manufacturers dealers get money out of it.
I let it cut in round town to improve air quality, but the fuel savings must be so negligible to most drivers that I'd worry more about saving my bank account of future repair costs than getting an extra couple of miles outta my tank of fuel.