Acquiring someone like Miller does a number things. One, it gives the Nat probably the best reliever in baseball. (At worst, top 3) Two, it prevents the Cubs/Pirates/Giants from adding him, obviously. Three, it solidifies the late-game bullpen, and while our ERA is fine right now, I'd feel better with Miller or Chapman in the 8th/9th than what we have now. It just makes us a lot better, and if there's one thing we should have learned from 2012 and 2014, it's that thinking things are "fine" because our regular season performance is adequate is not good enough. You can never have enough good players.