It is beneficial to other hubbers, especially for those with good hubs (since their hubs have an increased likelihood of being linked to.) If you link to a hub, it gives that hubber an internal backlink. The goal of hub karma is to get hubbers to link to each other in to increase the SEO value of hubs overall.
I don't know how important internal linking is since Panda, but I know it's one thing that was really beneficial in the past.
I do, on occasion, link out to other hubbers from my hub, but I do so only because it's a benefit to the reader and not to increase my hub karma. I've come across several hubs where you can tell they're linking just for the hub karma and not to improve their readers experience.
I see the point of hub karma, but I don't think it's the best way to get hubbers to link to each other. Hubbers who want to give their readers a good experience on their hubs will naturally link out (tastefully) to other hubbber's hubs. However, those just looking to raise their arbitrary hub karma score will do it not-so-tastefully. Since good hubbers will naturally link out to others without the hub karma, there's no point in having it. All it does is incite people to just link to random hubs without regard to their audience. That's just my two bits, though.
I hope that was helpful. :)