I'm a Jones fan so i don't like the trade but he had one year left on his contract and they likely weren't going to resign him next year so I guess they were trying to get something for him now rather than nothing.
Heres what John Clayton had to say about the trade:
Bears moving up: If you are trying to figure out the Thomas Jones trade, it's pretty simple. The Bears moved up 26 spots in the second round, getting a Jets pick at No. 37. That's a prime position to get a borderline rookie starter or a quality prospect. Why would the Bears have to give up a second-round pick and Jones to get a second-round pick? The answer is simple. The market for veteran running backs is at best a third-round pick. The Bears wanted to get a second-round pick alone but they couldn't. If you look at the draft value charts, the Bears gave up 280 points. That's the equivalent of one of the final choices of the second round or a top choice in the third round. In other words, they got the best value possible for a 28-year-old running back.
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I don't know if this is the best possible value, but according to Clayton it is.
Benson is a really good back, only problem is that he has proven himself to be a reliable back (three injuries in two years).