I was copying files from one large directory into another. I expected to have a bunch of duplicate files.
DO has an option to skip identical files. Unless I am mistaken, it is supposed to copy ALL but the same files. In my case it behaved the same way as just "SKIP", ie would only skip 1 file at a time until the next prompt.
Re Abr's suggestion, you do not have to use a different command just to skip multiple files, although you can if you want to (the only advantage being that you don't have to wait for the first Replace-File prompt). The command Abr suggests will skip all conflicting files, whether or not their dates/sizes are the same, which may not be what you want.