So he knows his opponents quite well. But with Brett Favre, the added benefit is that he will be joining a team and creating a lot of excitement and motivation. I've written before about events providing a serious energy and motivation jolt for a team. Notably, Mike Singletary becoming the head coach of the 49ers midway through last season and simply preaching effort and hustle.
With Brett Favre joining the team, everything will be amped up and done more energetically. There will be a real sense of hope and optimism. And that helps players practice and perform better.
So while his quarterbacking skills provide an upgrade, the sense of possibility will provide another bonus in terms of improved practice and player energy.
Lastly, I think that this team wide sense of energy helps players come back from injury faster and get sick less often. These are known benefits of people who are happier and more optimistic. It stands to reason that a greater sense of possibility will take players who are marginal and put them firmly on the side of enthusiastic and giving that extra bit of preparation. And in a 60 minute football game, it can often hinge on the most unlikely of players involved in the most unlikely of plays.