Seriously, though, have fun with the tag commentary if you like. But please try not to do that outside Tumblr. It doesn’t matter on this site, because its tags policy is crap anyway, but on other sites tag metadata is important to data organization and preservation, and users’ ability to navigate and hold conversations.
It costs sites like AO3 a lot of time, effort and money to clean up from Tumblr-style tagging.
SIGNAL BOOST.
Actually, AO3 isn’t particularly affected by freeform style tagging. There’s a great post about here at the Archive.
That’s only half the story on tags, though. Here’s the other post in that set, where they discuss a bit about the load that tags DO place on the system. In the case of AO3, the part of the system that carries the burden is the people, rather than the technology.
(Also, on another note, I find the information about AO3’s setup interesting. It’s kind of an experimental arrangement, trying to walk the line between the two ways of doing metadata.)