"Who tagged this?" was the only way to figure out who had added a tag, such as "fixme", so they could be contacted when the "fixme" was done. It also occasionally came in handy in other 'need to contact the tagger' situations, such as this DiscID tag which drives me crazy: http://musicbrainz.org/tag/1%2013%20165900%20150%207672%2022647%2034612%2048720%2059280%2074602%2087545%2095495%20107182%20131087%20141522%20153710