It makes the unpack function extract to a file name dependent directory. It is useful to enable maintainer to work with archives that contain all files and directories in the root directory of the archives directly, instead of a subdirectory.
That'd enable me to remove all the custom unpack functions from the kopano-* packages. Other packages use them for the purpose of extracting to specific dirs, too.
The following packages do that:
From a first glance, adding support for that directly would enable removal of the custom unpack function from those packages.