Tags are a useful way of filtering large numbers of queries or dashboards, but adding tags can only be done one at a time on each individual item. This makes the task of adding a new tag to a large number of items very tedious and time consuming.
It would be way more efficient if there was an action on the Queries list (for example) to add a tag (or tags) to multiple queries at once. The list of queries would need have a selection box to enable the user to select the target queries and then apply the selected tags.