mocking and quoting bigots I've seen so far
:liberalism: turns to 
"you know it's hexbear when the tankie pronoun parade shows up to force pictures of pigshit in front of you!"* real quick
[*this is paraphrased, I can't remember the exact original quote]
Or "so suddenly I'm Hitler because i think people calling themselves Fae gender is dumb"
Or "why should i need to learn a new set of different pronouns for every person I meet?" (this followed two comments after "I'm literally not a transphobe, I work with plenty of trans colleagues who feel safe around me" (average lib being scratched in real time by having to acknowledge neopronouns))
.
All of these shitheads claimed to be allies when they started interacting but our brilliant pronoun tags immediately made them out themselves as the bigots they are who only pretend to be allies because it looks bad to be openly and proudly transphobic
TL;DR: 
It makes some people that are comrades happy and takes basically no effort to just have them there.
As a bonus it makes chuds mad.