When you buy a brand new bike you might well be advised to use semi-synthetic oil rather than the fully synthetic high grade stuff for the first 1500 miles at least.
On BMW bikes you may need to use the lower grade of oil for sometime longer.
In fact it actually stated this in the owners manual of my former new Honda CB750(very similar to a Nighthawk)
The reason is that the engine has to be run in first, and using some of the very high quality synthetic oils not only slows this proces down, it can lead to burnishing of the cylinder bores, also known as glazing.
Cylinder bores are not polished mirror smooth, they need a certain amount of minute scoring in order to hold oil on the surface.Glazed bores will mean that an engine will use a lot more oil, very much like Hermann Cheruscan’s case he describes.
Taking the glaze off(glazebusting) is very expensive since the cylinder block has to be removed so that it can be fine sand or bead blasted.
Old engines have much greater(in relative terms) clearances internally either becasue of wear, or because manufacturing tolerances in older engines are greater, in an older design of engine it is inadvisable to use fully synthetic oils, which work extremely well on high revving, high compression, and close tolerance engines.
All that said, Ford makes and sells a small car here called the Fiesta, which is fitted with the Zetec engine.
They specified around 10k miles between oil changes, then suddenly changed that the following year to 20k miles.
The onnly differance was that the oil specified had been changed to fully synthetic type.
This does not change the fact that other parts still need servicing at 10k miles, just that the service intervals were extended.
One example of how disastrous this can be, the toothed belt driving the cams, and water pump etc was inspected every 10k for signs of damage.
When the service interval was changed to 20k to suit the oil regime, it meant that cam belt was inspected half as often too, and this leads to more risk of it snapping, and when it does it is disastrous.
In the UK a 20k service interval on a small car can mean that belt does not get inspected for maybe two years, the belt ages and the risk of failure is much greater, and there is a liklehood the vehicle is out of warranty too.
Often such cars are sold on well before that 20k service, so the potential used car buyer has lots to worry about.
Given the cost of a service is around £120, it seems silly to me to risk a total engine write off costing up to £1500 or more just for the sake of a few litres of oil and a cam belt.