In addition to bulk tagging operations available via the right-click contextual menu in the draft list, drag and drop can be a handy way to organize one or more drafts.
Drafts selected in the list can be drag on top of a tag in the tag filter list to assign that tag to all the drafts, or drafts can be dragged to the folder selection buttons to either assign flagged status, or move the drafts between the inbox, archive and trash folders!