You refactor some code before doing a bug fix, you clean it up to better understand how it works, and leave the code in a better status than you found it, in purest boy-scout style :P.
Then you move methods to a new class in a new file. And later make some modifications to the moved methods. Easy, uh?
Well, Plastic SCM can now track the refactor and diff it correctly, because we have just implemented multi-file semantic diff or "analyze refactors":
This is another step forward towards semantic version control as we explained about one month ago with our initial release.
Now Plastic can track moved code across files, and soon we'll apply the same tech to merging.