I am honestly not sure about both of these. Last year I attended Porsche e-school driving event where there were several Porsche engineers with whole event being only about Taycans and Macans. I specifically asked during one of the technical workshops about auto recuperation as I seen conflicting information about when it is beneficial to activate. Engineer confirmed that while the option is there they don't believe that it is good idea to have it enabled on highway or drives with constant speeds as it is more efficient for car to keep rolling than to being constantly slowing down by recuperation and then speeding up again which will always have some energy loses. This function is in their words there for city traffic or if car is going for prolonged period downhill.
I tried doing multiple highway drives with it on and off and honestly I have not noticed any significant difference in consumption. But then again like I mentioned my car seems to giving me random numbers on consumption and its scheduled for check.
Regarding cruise control, while you are technically right I don't think there is much difference in consumption at least not directly. Car unless you manually deactivate every security feature is already checking for obstacles in front of it, centering the car in lane and is also reading speed signs even without cruise control being activated. I am guessing there might be higher pool rate of all these sensors when cruise control is engaged, but I would imagine that would be a small difference in energy consumption. But yeah if you want to conserve as much energy you can turn off even things like ambient lighting, HUD, passenger display or even audio (I noticed that Bose app has even power saving QE preset) or analogue clock. From my experience all this has negligible impact on range/consumption. And yes I have experimented with all these in order to figure out what is happening with my car.
Now with all that said I believe that difference that you are seeing in consumption with cruise control on/off is mainly down to traffic that you encounter. While car lets driver set distance to the car in front of it I noticed that it probably as a security measure is quite cautious and starts gradually slowing down before human would. What is also not clear to me is whether cruise control is also for initial portion of slowing down using recuperation or for security reasons it always goes for normal breaking. This was never clear to me even in my ICE cars with adaptive cruise control. Seasoned driver will just take their foot of the gas and will not hit breaks every time when there is something in front of him if there is enough distance. Yet since car has no contextual data, like if it is in the moment going downhill or uphill, therefore cannot with 100% certainty be always sure how fast it will start slowing down just by releasing gas I would expect it always going for breaks. Either way since I am paying attention to the road I tend to change lane even before cruise control starts slowing down which is also the reason why I am able to have rather constant speed.
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Elevation change has a big impact.
