Perhaps the biggest benefit of getting Barwin is that round one (or just possibly round 2) of the draft would not almost have to be a pass rusher.
I used to think that rounds 1,2,3 of the draft were likely to be pass rusher, corner, tight end, in some order. If Barwin was signed, to go with TE Bennett, those first three rounds are much harder to predict. Then it would probably be cornerback, ?, ?. The Packers might still go OLB/CB/TE, even with the additions, but it gives them options to go somewhere else, like WR, RB, ILB, DE.