Jeffrey Loria, whom you might know as Azazel, Beelzebub, Ol' Scratch, or by his given name "The Great Satan, Dark Lord of the Underworld" has commenced gutting a Marlins team he put together roughly 12 months ago in order to justify fleecing the city of Miami into building him a new stadium. ("But it'll help revitalize the neighborhood!" says stupid people who don't understand that that happens when the city puts money behind a well thought out neighborhood plan with or without the existence of a local sports teams home field). Outside of a few moronic sabermetricians ("Their marginal win per dollar spent will go through the roof!") everyone thinks this is terrible. Unless of course you are a fan of the Nats, Phillies, Braves or Mets. The Marlins weren't good last year and they'll be worse than they needed to be for the next couple of years. That means more wins for these teams.
For the Nats especially this will help, because this down time for the Marlins coincides directly when the Nats will be fighting it out for everything from Wild Cards (hey, the Braves could have a good year) to home field advantage. But how much will it help them?
In 2012 here were the NL East teams records vs the Marlins
WSN : 9-9
ATL : 14-4
PHI : 10-8
NYM : 12-6
Both the Mets and Braves aren't going to necessarily gain much from the Marlins destruction in comparison to this past year. It will help them in that they won't lose more games, but if the Braves and Mets want to get more than 94 and 74 wins respectively, it's not going to come just from Miami becoming a doormat in front of them.
The Nats and the Phillies though, I think both these teams can probably expect 2-4 more wins just because of this. That doesn't mean the Nats are definitely looking at a 100 win season. There is WAY too much going on to say that. But they should definitely bounce back against this team over the next couple of years giving them a nice theoretical cushion to start the year (While other teams may have had some bad luck vs the Marlins this year, Pittsburgh going 1-4 for example, anything can happen in 6 games. Even the worst team has a winning record vs somebody and even good teams have bad stretches vs also-rans. So you can't say Marlins are worse, Pittsburgh will win a couple more games. Play a team 3 times that many times though and you start to get a proper comparison)
Is this automatic? Of course not. The Nats could go 9-9 again next year. Hell, they could go 8-10 or 7-11. It's not impossible. But trades like this make those results far less likely. The needle has moved for the Nats, from an expected record against Miami of something like 11-7 to something like 13-5. That may not seem like much but remember the Nats won HFA by two games, the Cardinals won the 2nd WC by two games. Every little bit helps. This helps. So thank Loria right after you splash him with holy water and watch him burn.