The workbook tag should be excel - even the wiki for this tag says it's excel only:
A workbook is a native Microsoft Excel spreadsheet file containing discrete workspaces called worksheets on which calculations are performed.
There are 87 questions tagged workbook and 64 of them are tagged both workbook and excel. I think that calls for a clean-up, not burnination.
workbook
are about Excel, not all of them are. Most of the rest are simply poorly tagged or are just bad questions to begin with.