I came to my A3 from an LCI BMW 3 series that had start/stop. I've always been of the view that no matter what BMW say about uprated batteries, starter motors, active battery charging blah blah that stopping and starting the car often is not going to be good for it, to that end I always switched off the stop/start function.
My A3 has the same function and I also switch it off, I just cannot see how it can do anything other than put parts under greater strain than they need to be.
When I had the beemer I ran it stop/start for a while and monitored mpg, then switched it off and there was barely any difference anyway.
So, who leaves it on, or like me do you err on the "mechanically sympathetic" side of things?