I use it the same way I did on Reddit; it's a decent gauge in how willing I am to engage with that person. If their history is littered with downvoted posts, then I'm less likely to engage because it's more likely they're being inflammatory on purpose.
Karma systems don't make places worse; the value placed upon them by the users does. It's not meant to be a counter for how liked you are, it's supposed to be representative of how you interact with the community; bad karma for bad interactions. But people use downvote as a disagree button, and people spam posts cause "big number make feel good". Good idea, difficult implementation given how humans work.