I understand that a tag's name should make it clear what the tag is for, but this is often not the case. For example, we now have grammar and grammaticality. Users will probably need to read the tag definitions to decide which one to use. Myself at least find the explanation text indispensable. Some tags lack this text, however, so could we make it mandatory to provide one when coining a new tag? If not I can only hope someone smart and keen will volunteer to go fill in all the missing bits.
Tags descriptions are not mandatory, as they should be provided only for tags that could lead to misuse because the tag is misunderstood, or for tags that have been already misused.
I once found a question on meta.SO about when a tag-wiki is appropriate; I don't find the link right now, but I remember it was reported that not all tags need a wiki.