I'm not a big user here, but here's my two cents:
I could see highlighting certain specific game terms, when they are a big deal to the overall context of the post. Like, I dunno, highlighting class abilities for D&D 3/4 does make the text a bit more readable in some ways. It sorta stops you a little and says, "Here, here is the thing you should look up." Actual links to some kind of reference thingy would be preferable, though.
It seems absolutely pointless to highlight fictional place names.
Coming here without any foreknowledge of the site's style, seeing
lots of highlight text in one paragraph was
really jarring and didn't really make
the text easier to read.