Nocioni comes off the books. You include him in order to get more cap space.
Allen also comes off the books, so after this year, we will not have a good SG.
Yes, it does make it harder to make the playoffs this year, but Boston isn't winning a championship this year. That's the whole point of this trade. Get Evan Turner and a TON of cap space. Start over with Rondo, Turner, and draft picks. Throw money at Love or Howard and see what sticks. If you have to go through one rebuilding year next year and get another high draft pick, then do it. Throw money at two top 2013 Free Agents.