The Patriots are a team that has struggled getting pressure on the quarterback, and so they've just added a big piece on their line. Kelly is 32 but was said to have had a considerable amount of interest once he was released. This was a big get for the Pats.
Now the question is, can he succeed where Haynesworth and Fanene failed? One thing that will help is his durability. Kelly hasn't missed a game in five straight seasons. He'll be a big veteran presence on the line that can move to DE if needed. His production did dip last year(only 1.5 sacks) but in the two previous he had 14.5 combined.
The move also allows the Patriots to focus on other areas in the draft. One mode of thinking was that they could take a defensive tackle in the first round since their other positions of need were so deep. Now, you might be able to cross that mode of thinking off the list. The Patriots can safely trade out of the first and pick up players to continue to overhaul their secondary and wide receiver positions.