Was unable to find rationale for separate tags accros SE sites.
Tag function According general definition in information systems, a tag is a (unstructured) keyword or term assigned to a piece of information (such as an Internet bookmark, digital image, database record, or computer file). This kind of metadata helps describe an item and allows it to be found again by browsing or searching. Tags are generally chosen informally and personally by the item's creator or by its viewer, depending on the system, although they may also be chosen from a controlled vocabulary.
tag origin and quality
Where from tags are originated and what are tag quality parametres?
problems and contradictions examples related with SE tags
Humanity is facing information overload. SE sites are created for collecting and sharing personal knowledge on questions or problem solving. But tag's descriptions are not matter of personal knowledge - it's just matter of /word-meaning/, i.e. vocabulary/dictionary, or taxonomy/ontology or, speaking in general, human lexic conceptual apparatus / framework. So why time has to be spent on fact's duplicating and sharing?
At the same time We are living at the linked data times. IMHO it's the biggest blunder having same tags with different descriptions in different SE sites unlinked. Tags (and so - descriptions) should be unified.
So I'm calling to unify all tags across SE sites as feature request. Maybe automatic linking to Wikipedia and/or some other decent dictionary would be reasonable.
This is not a duplicate of Could the tagging system be enhanced to support tag synonyms?