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!

This leads me to three other questions:

1) If you use the bike every day, is rust
really a problem for either chain or
sprockets/chainrings?

2) What material are they made of?

3) When you buy a brand new chain, it is
factory impregnated on the outside as well.
Is this again only to prevent rust, and does
not help shifting or reduce wear in any way?

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underground experts united
http://user.it.uu.se/~embe8573