They tried shooting on Empire with Peter Mayhew's stand in when he was completely exhausted from long days with Threepio on his back. It became obvious how much Mayhew's mannerisms are part of Chewbacca, and they could only do long shots or keep Chewie's back to the camera until his return.
The Clone Wars animators actually had Peter come in so they could get Chewie's moves right for the show.
Even Creepy Puppet Yoda has a leg up on his digital counterpart, because that's still Frank Oz hiding under the floorboards.
When Hasbro had live action footage shot for a Star Wars video boardgame, they got Prowse for Vader.