The efficiency and productivity tags have no tag wiki, only 5 resp. 8 questions, and (especially the first one) are not used in a consistent way. I can see some point in focusing productivity on tips & tricks for using Stack Exchange, but we could also use tips for that (that tag lacks guidance too, by the way). Thoughts?
Just to update here.
I started work on re-tagging as there appeared to be a consensus that this was worthwhile. Subsequently a dissenting view appeared here and some of my edits were rejected from the Suggested Edits queue. I have therefore concluded that the consensus was more apparent than real and have stopped the re-tagging process. I have contributed wikis for the two tags which seem to cover most of the cases tips and cost.
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Let me make a concrete proposal for comment.
If there is a common theme behind the efficiency and productivity tags it is people trying to improve their personal efficiency in using the site. They are not asking how to make the underlying software more efficient. It is therefore hard to see any difference between that and asking for tips about how to use the site so I would propose that all three sets of threads could be combined as tips. I think one of the questions asks about tooltips which is slightly different but tagging is never perfect.