Almost always there is a pattern of dirt, like
the "negative" of the chain, on the
chainring/sprocket. This is often very loose,
a wood stick and then rotation will remove most
of it in but a few rotations.

Question is how much this really
influence anything?

Once removed, there is a slightly better feel
to pedaling - but I don't know, maybe it is
all psychological?

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