Any idea?

 

My dealer told me to use it when I have the 16 spare on.

 

I turn VSA off when I am mostly on city roads, not many corners. If I am on a rural highway (especially one I am not familiar with), or on a freeway, I leave it on "just in case".
I wouldn't mind going to a track and doing a few laps with it on, and a few with it off to see the differences in times, and also how the car feels in both mode. Maybe after I get springs and sways.

 

Same here. I don't recall if the manual made a reference but I was told that different tire sizes on the same "axle" would cause the VSA to think one tire was slipping and try to correct. It makes sense to me.

I've never had a flat and I've never turned it off except to see if the light worked. It did.

 

I was reading the manual the other day and noticed something I missed before: the warning light comes on if you overtemp your brakes! Yet another reason to leave VSA engaged.