Purpose of "bicycle=yes" outside cities

The wiki page here (http://wiki.openstreetmap.org/wiki/Key:bicycle) redirects to a rather elaborate page that explains how to set the various bicycle-related keys for cities.

However, I am mostly interested in riding outside cities; so the only applicable guidelines are (taken from http://wiki.openstreetmap.org/wiki/Bicycle)):

bicycle=yes: Where bicycles are permitted, overriding default access…
bicycle=no: Where bicycles are not permitted, ensure this is indicated

I guess in nature, the default is that bicycles are permitted, so “bicycle=yes” seems meaningless. However, I have seen that key set for quite a bit of ways (http://overpass-turbo.eu/s/8sb), and I wonder whether it has some meaning, or (if it doesn’t) can be given a meaning.

Perhaps, we should mark a trail with “bicycle=yes” if it is used for cycling, but not enough for “bicycle=designated”?
Maybe, we should mark “bicycle=yes” when a trail is passable by bicycle, but we cannot be more specific with e.g. “mtb:scale=2”?

Right now, my opinion is that we should never use “bicycle=yes”, but there is no point in removing it where it already exists. I am not satisfied by this resolution. Please help me by expressing your opinion.

I think with tracks we shouldn’t bother.
With paths, my feeling that it should be no if it’s forbidden or unrideable, yes if it can be ridden and is not forbidden and designated if it was built by riders or for them and used primarily for riding.

I think that bicycle=yes is not of much importance.
What is important to tag is:
(1) bicycle=designated “Where a way has been specially designated for bicycle use” by kkl or others
(2) bicycle=no “Where bicycles are not permitted, ensure this is indicated” (example: road 1 or 6)
We should note that some trails are mistakenly tagged as bicycle=no, probably because some one thought that that this is the way to describe a non ride-able trail (non ride-able trail should be tagged mtb:scale=6)