On Tue, 06 Nov 2018 20:12:37 +0100, Emanuel Berg wrote:

OK, so if IIUC, oil (a light coating) on the cassette/chainrings and on
the outside of the chain does not facilitate shifting nor the entry/exit
of the links onto/out of the sprockets/chainrings?

The only reason to do it is to prevent rust!

It makes the works quieter.
The grinding of metal on metal is work wasted.