Some historical perspective on the subject. I went back to 2008 and looked at all the post-trade deadline free agent signings by the four teams that advanced to the conference finals each season. These are the players that were rotation players for their new teams for even part of the playoffs:
2008:
Detroit: Theo Ratliff
Boston: PJ Brown (greatest impact by any such player on an eventual champion, IMO)
Spurs: Brent Barry
2009:
Cleveland: Joe Smith
2010:
Boston: Michael Finley
2011:
Miami: Mike Bibby (starter in the playoffs)
2012:
Spurs: Boris Diaw (starter in the playoffs)
OKC: Derek Fisher
Boston: Ryan Hollins
Miami: Ronny Turiaf
2013:
Memphis: Keyon Dooling

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