If the edit to the question is simply a change in tags it shouldn't be approved except in the following two cases:
##1. The Question clearly is mis/poorly tagged
This will be more of a rarer case than you think, because if the question is poorly/mis tagged then more than likely the content, and title of the question is of the same low quality.
##2. The tag is a part of the tag cleanup movement
This will be more likely of the two scenarios. You can tell if the tag is decommissioned by hovering over it and looking at the description for the text:
DO NOT USE - Removed as part of Super User mid 2012 cleanup - Super User mid 2012 tag/question cleanup