Depends on the frequency of cameras, if it is just at the on and off ramps of a motorway, then one could exceed the speed limit for most of the way, determine how much time has been saved and enjoy a tea break at the service station before the last exit.

On a whole day drive that would still be faster as the speeding means you don't have to add on time for breaks.

In France that's effectively what happens. The toll gates are used to determine the average speed check over a journey, and so you can notice that the last service station before a toll gate is busier.

Not that I had a chance to do the same in the clapped out old Volvo I drove through France in.

I personally think average speed checks are great. In London I'd love to see the congestion charge cameras (number recognition technology) also used to check for average speed between any two cameras. I think that if people knew the whole of the city centre had average speed check enforcement that it would be a great benefit to the safety of pedestrians, cyclists and other road users in the city.