I think they are part of the Gamification attempt of Discourse.
In games it is common to get badges for special “achievements”. … It’s OK, if you don’t care, but there may be users that actually like it, to be reminded that they have achieved something. Even if it is the information that a post they created was liked 10, 20, 50 a 100 times. …
As I wrote at: To Admin: Why Don't Some Posts Have A Reply Button? - #14 by pmario there are some badges where I’m actually proud of. …
If someone takes the time to write a reply to a question, posts links to related topics or other pages,
with the intention to help other users, I think – No – I know, that it feels good if you see, after some time, that it actually made a difference. …
Not only for the user who posted the question, but for others too, that liked your reply or followed your links.
As Boris pointed out, there is an overview, about the existing Badges and what they mean. I’m sure there is room for improvement, if we want to invest the time.
The existing Badges “come for free” and I’m sure that for some users they will actually will mean something after some time.
just my thoughts.