Not sure how much harm stop/start does to the engine when driving about town relatively slowly as the engine, starter motor and battery are designed for that but I worry on the motorway or any other roads where your driving relatively fast if you have to stop you do not want the engine to stop as the turbo is still very hot and spinning very fast which requires a constant supply of oil for lubrication and cooling, I always switch off the stop start out of town. This is not as important on diesel engines as the exhaust temperature is cooler and the turbos don't generally spin as fast.
