In addition to reasons, tag descriptions can provide deeper context to the meaning of a tag when it is the same in every occurance.
Reasons still have a place in the mix to describe why the tag was applied to that specific article (or item), describing the context in which it was applied, not the overall meaning.
A great example would be using Traffic Light Protocol flags, we could have the name of the flag simply be "TLP:RED", with the description articulating "For the eyes and ears of individual recipients only, no further disclosure."