A high Karma shows you how active a user is. Basically a higher Karma means the user takes part of discussions and this usually means he gives something back (knowledge, thoughts...) which is increasing his Karma.
I personally don't see the use of karma. It seems like another way to differentiate users (similar to what a post count does) and many forums seem to move away from that.
But then again if you want to offer crowd-sourced support a user with more karma can be seen as a more valuable member with a higher probability of providing a helpful answer. Doubt there's another reason for it...
Comments
do we get a free license of a GSA product of our choice if we reach ∞ karma?
http://www.youtube.com/watch?v=JmcA9LIIXWw
Edit - now it's gone again
Edit 2 aha! If you edit a post your Karma shows??
Lucky there aint more of your kind on here or it would be another group from the same era
Flock of seagulls
Still no Karma showing
Edit. This ones edited
I came across it today while I was just staring at my profile (Dont know why I was staring or what I was thinking :v)
http://prntscr.com/5fjt0p