Some midseason trades are remembered as the finishing adornment for success -- at least after the final pitch was thrown. The Blue Jays swapped a couple of prospects for David Cone in a stunning late-season trade in 1992, and because Toronto went on to win the World Series and the deal worked as designed, nobody ever cared that one of the two prospects surrendered was Jeff Kent, who went on to have a Hall of Fame-caliber career.
The Giants traded for Hunter Pence in July 2012, and because San Francisco dogpiled at the end of the World Series, we remember Pence as the perfect addition at the perfect time, and the aggressiveness of general manager Brian Sabean as pivotal. In 1996, the Yankees traded for Cecil Fielder, and he was important to what the team accomplished late that year. There’s almost no way the Yankees would’ve won the World Series in 2000 without a trade for David Justice that summer, because there were times that Justice seemed to carry them.
But there is the dark side of midseason moves, of course. Almost all of them are thought out and built on logic and sound analysis, yet many of them don’t work as intended.
I remember sitting on the set of "Baseball Tonight" after the trade deadline in 2007 and echoing the prevailing sentiment that the Red Sox were one of the big winners of the midseason dealing period, because they had landed the reliever perceived to be the best available -- Eric Gagne.