IRC discussion: http://chatlogs.musicbrainz.org/musicbrainz/2013/2013-11/2013-11-10.html#T21-09-55-136100

It is not uncommon for artists or labels to host a party or reception or other type of event related to the release of a Release or Release Group, often featuring performances from the Release in question too. This would be a way to record this until we get proper Event entities.

Proposed wording:
<Release>/<Release Group> had launch event at <Place>
<Place> hosted launch event for <Release>/<Release Group>