A request is for the addition of a "Last used" property to the tag (i.e., this tag was last * applied or removed from components on mm/dd/yyyy @ hh:mm:sss *)
The task for cleaning up tags uses "Tag creation days:" and "Tag modified in days" as the main selection process. Due to the volume of development the count of unique tags could be quite high. Due to the varied iteration and release schedules we have, the length of time that a tag could be valid for could be range from two weeks to indefinitely.
Because of those two observations I am suggesting two changes to tagging. One change is for the tag, itself. The other is for the Admin - Cleanup tags.
The first is to detect and make visible when the tag was "Last used". From a tagging perspective that would allow us to base tagging clean up on something other than the creation data and last modified date.
By adding "Last used" property to the tag and as a condition in the "Admin - Cleanup Tags" task, we would have a way to avoid the clean up of tags that are still part of a longer iteration or a release which is a risk when cleaning up tags based on creation or modification dates.