I was looking at the new questions when I noticed this question which had three tags including elevator and lift which seemed to be proposed by the person who asked the question. Since these did not seem like helpful tags I retagged the questions and removed the offending tags. I then went to look the other questions they just asked and saw that they also proposed a greeting tag.
This is what stumped me, we don't have a greeting tag, it seems a little bit localized but there are a number of questions about greeting others. The tag feels useless without all the old questions not allowing it for that reason would would kind of defeat the point of making a new tag at all!
So when is it appropriate to make a new tag and if you do, should you go an retag all the old posts to which it applies?