To steal David's description,
The idea here is that Bumble is a blogging/CMS system aimed at people like me who have lots of different interests and projects. Using tags and tag-specific RSS feeds as well as section-specific feeds, people can view / subscribe to the activities they actually care about - say my pen and paper musings or news about SE:SS but not my political rants...
On Katzenfabrik, I've been using subsites to organise my posts more than tags (see the top of the main page for the list of subsites here and other websites where I have a presence). You can use tags, though, to follow my thoughts on Switzerland or on vampires, for instance.