Vizient presented Hierachical tags to their user group and many found the below example confusing. In their opinion, when searching for a tag all "children" tags should automatically be selected when searched.
Additionally, they found it confusing in the below example if you click on the Parent Tag, you’d get 23 records in your results set. If you clicked the Parent Tag and the Grandchild Tag, but not the Child Tag, you would still get 23 records.
Their worry is that some users may try to click on the Parent Tag and then the Grandchild tag expecting a narrowed results set, for example, but they would still get the same results as if they only clicked the Parent Tag.