Currently there are ongoing discussions in the german arm of the wikipedia about the relevance of certain articles. Some people think they should be deleted because they are not relevant enough to be mentioned in an encyclopedia.
While Openstreetmap has different and arguably harder to solve problems in other areas, we fortunately do not have them in this particular case.
As a matter of fact, we simply don’t even try to rate something as relevant.
If you want to put an object into our database, because it is relevant for you, then you are welcome to do so. The now infamous discussion on the german mailinglist about dog-excrement-bags comes to mind.
The only thing where I could imagine a simular discussion is one about particular objects to be rendered in the standard map style or not.
There is only one reason for objects to be deleted from our database. They are nonexistent on a particular place, ever were or ever will.
If they are non-existant anymore (e.g. stuff like disused railways) they have to be marked as such. Pretty black and white stuff as you can see.