He is a good player but not the center piece of a contender. Similar to Chris Bosh in Toronto. He averaged 24&11 in 2010 (much better than Horf). Horf would be a perfect Robin though.
He is a good player but not a good fit for this roster unless Horford plays mostly center. He is probably signed as a future trade chip. Well whatever...
That's a very young team. I think tanking is great for them; give playing time and responsibility to youngsters. Next year they will probably have a very good draft position and a lot of cap space.