It LIMits the maximum speed you can travel at. I set it at 30 in town, therefore never risking a speeding ticket (except where the limit is 20).When it is lit up, you set the max by hitting the Cruise control up, etc.
Very very useful feature. I use it all the time on the average speed section on the M4. I set mine to 52mph which is a GPS verified 50mph and i and waft past everyone who who is doing just under 50 on their speedos, magic.
I don't understand people who zoom and brake for the average speed cameras, however. They were obviously smoking behind the bikesheds when their classmates were being taught that Speed = Distance / Time.
Hit the limiter a few times in the CL and no LIM (although the last owner had set it at 120mph and when I ran into it on the first autobahn run I thought "WTF!, I have broken the car"
Why he had set it at 120mph and have never taken it out of the UK, I don't know......