I use CC with the satnav on so I can keep checking exact speed, it sometimes bumps up a little by one or two but I usually set it for 97-98 in a 100 zone or 77-78 in an 80 zone and so on.
My sat nav alarms if I go over the speed limit and it rarely does if I am on CC.
It more often than not goes off if I am driving around suburbs, towns etc when CC is not on.
By the way to the other poster statistically there are lots more accidents/deaths etc on local roads/suburbs/towns etc than on motorways.

Just been reading a very long discussion about the CC on our particular model and turns out you can more efficiently hold speed downhill with CC off as it does not throttle off completely.

Don't use the CC much so I hadn't realised ... hmmmm ...