Mark has it right ! … Unless you are on long stretches of reasonably flat road it’s pointless, I often use it in such cases but only to relax my legs a bit, it can be a real pain in the ■■■ on my truck because it is linked to the radar system so when getting close to something in front it will slow to their speed unless I see the vehicle is moving slower before the radar tells me and move to another lane to get past. I find that it does nothing to aid fuel economy, it means that fuel is being pushed through the system constantly, it also slows up the vehicle going down hills, when it is not in use taking my foot of the gas mean no fuel (apart from a tiny amount to keep the engine going) is being used, my regular run from NYC to St Albans VT uses an average 7.5 to the gallon when loaded and going north, if I use cruise as much as I can it usually comes down to 6.5.
Pimpdaddy:
I use it everywhere I can, love it.
+1, I’m getting Lazy in my old age. Lol.
On the Actros (if the company pay for it !) it’s got GPS Cruise Control where it maps out the road ahead then does all the gear changing in advance i.e. just coming up to the brow of a hill it lifts off.
The Merc Trainer’s teach you to use CC most of the time as they say that the ‘Puter’ knows best, it only uses as much Go Go Juice as it needs. Nice piece of ‘Expensive’ kit.
What you save in fuel, you spend on Tech.
I’ve never used the flashy ones but the basic works for me:)
All the old ■■■■■ won’t use it as they reckon you’re likely to die if you fall asleep with it on whereas if you don’t use it and fall asleep then your foot lifts off the accelerator and you eventually come to a halt. 
Heard loads of them use this argument so if you come up behind one of those annoying ■■■■■ that keeps speeding up and slowing down it’ll be an old ■■■■ driving it and for the above reasons most likely.
If its basic CC then i usually only use it on long stretches of m’way and get up to speed then switch it on and let it take control…then I try and think of something to do so I can exercise me legs, usually some sort of dodgy riverdance thing keeps the blood flowing.
Smart CC I would use more often unless I felt it was making a meal of things with far to many gear changes.
I remember when CC was a high cost optional extra suppose a time will come when the driver is an optional extra.
Yep are meant too use it too get f/b,but don’t on long haul,back early hours,as I always think if I fall asleep I’m just going too go straight off road and into field and keep going until I bog down,hit tree etc
Whereas if it’s not on hopefully as I doze off ,foot will lift of throttle and I stop before I run off road/ hit something .
The DCPC man told me that the examiners want to see C.C. used on driving tests.I use it on duals and Mways.The T.Ms. ought to be promoted drivers instead of college boys.