I think what this does is bring the outfield's close in production between Nats and Braves. I think Span > B.J. Upton, Harper = Heyward, Werth = JUpton. Offensively the Braves have more home run power there, but Nats have less K's thanks to Span. Both are stupid athletic and it will play well.
What is bad for the Braves is the loss of Prado, and now the lack of a leadoff hitter falls on Andrelton Simmons, much like what the Nats did to Desmond and everyone else on the roster. I think there will be an issue there considering they don't have a Werth like guy who can slot in if Simmons falters.