They are not designed as general purpose tools. Key is a directory to copy from, value is a directory to copy to. The read and the written file may be identical, but on AFS it is quite likely that people are installing to a different directory than the one where the files later appear. This is useful for binary distributions. Filenames with the extension pm are autosplit.
Second argument is the autosplit directory.
If third argument is not empty, it is taken as a filter command to be ran on each .pm file, the output of the command being what is finally copied, and the source for auto-splitting.