First off, the Cavs did not trade Luke Jackson for Dwyane Jones.
Well, technically they did but actually it isn't about the player swap. Its about accounting, roster flexibility and granting a player's wish. Let's break it down.
--The Cavs had too many guards and not anywhere near enough playing time. They've been in talks to move one or more of the them for months. Jackson's multiple injuries have both cast a doubt on his future and led by to be passed by as the Cavs have acquired a glut of guards. Jackson had been asking for a trade for the last year or so.
--The Cavs get a prospect in Jones, a guy who is a decent defender and a good rebounder. He led the NBA D-League in rebounding at 11.7 per game last year. There's a good chance he'll be back there this year. Jackson was not eligible to play in the D-League.
--Now the numbers, Jackson will make $2.1 million this season, Jones will make $664,000. To make up the difference, the Cavs sent the Celtics $1.4 million. Both deals are guaranteed. Before the deal, the Cavs were less than a million below the luxury-tax line of $64.5 million. That limited what they were able to do to add to the roster. The Cavs now have more than $2 million under the tax line.
--Being creative, Cavs GM Danny Ferry actually made two deals. He traded Jackson and the cash for a $2.1 million trade exception, which is good for one year. It means the Cavs can now trade for a player worth $2.1 million or less for nothing or combine that in a deal. Then he took on Jones, who the Celtics were looking to move because they want to keep Michael Olowokandi, for nothing in return, which is allowed because Jones just makes the minimum. The NBA just treats it as one deal.
Hope all that explains it for you.