If we know that valves control the flow of air and fuel, into the cylinders and exhaust out of them. And when and how long the valves open (timing) and how much the valves move (lift) both affect engine efficiency. Did you noticed eny increase in fuel consumption whan you have to adjasting valves? I did not whith 45 000 km on my odo. I ask because I whish to skip open engine and checking valves.