So BMW uses VANOS mainly for efficiency not for power. Exhaust gas is inert, and doesn't have much oxygen for combustion, the DME uses the VANOS solenoids to control the valve opening time to create a slight overlap between the exhaust and intake cams.
This will allow some of the exhaust gas to recirculate back inside the cylinder, and go backwards towards the intake manifold, instead of having all of exhaust gas escaping out of the exhaust valves.
On the next combustion cycle, when fresh air comes through, the cylinders won't be completely filled up with fresh air, they'll be partially filled with fresh air and partially filled with recirculated exhaust gas from the previous combustion cycle.
This effectively reduces the engine size, because exhaust gas is inert, so if you fill 20% of the cylinder capacity with inert gas, you've effectively reduced the size of the engine from 3.0L down to 2.4L, so it improves fuel economy by making it behave like a smaller engine.
The above, is why BMW has never bothered with all these cylinder deactivating/disabling techniques that American and some Jap car manufacturers applied to their engines.
Downside to the above, the engine head runs hotter when EGR is active, because the exhaust gas is very hot obviously. The other discovery, a friend of mine found out that if the EGR is disabled, the engine doesn't require to be walnut blasted as often. The theory is, the hot exhaust gases flowing back through the intake valves, cause the oil film on the intake valves to get caked on the valves forming that solidified carbon powder you see on the intake valves and ports. After disabling EGR, intake valves look spotless after 13,000km. They just have a slight grey-ish shade, I'll wait till I've put 30,000km on it since reducing EGR and recheck.
I didn't it disable it completely, only just reduced it by significant margin. I haven't been paying attention to fuel consumption, so I can't comment on that, but I reckon there'll be a slight increase with EGR reduced. Wrong cars to buy for fuel economy anyway haha
When the engine is underload, or any situation where you're hard on the throttle, the DME disables EGR immediately and cylinders gets fed fresh cold compressed air for best power output.