Not every string will be an entity, otherwise it would be turtle-entities all the way down :)
We need entities whenever there is some thing that should have identity.
The naming conventions specified in linked data best practices help to remind implementers whether the predicate should have a literal or a resource as its object. Datatype properties should be nouns, Object properties should be verbs. Bibframe is currently very inconsistent in its naming, and tidying this up would be a great benefit.
Which is not to disagree that documentation and examples should be available, comprehensive, consistent and clear.