First post, so I'll be brief on my opinion. I would say "it depends". To communicate between people and even to clarify one's own thoughts, a formal language, with an appropriate lexicon and symbols, is a key facilitator.

As for desirability of audience, the About page says "Less Wrong is an online community for discussion of rationality", with nothing about exclusivity. I would suggest that if a topic is of the sort that newbies and lay people would read, then English is better; if more for the theorists, then math is fine.