Password Policy: The installer adds a Password Policy basically enabling Universal Password for the driver objects. This way, policies and processes can retrieve passwords off objects in the driverset (Jobs? Driver object itself?). But of course, password policies only inherit one layer deep unless it is assigned at a partition boundary.
Ergo, a valid reason for having it partitioned. Took me a while to find this one though. With PCRS and new policy approaches in 4.5, this is actually more important than ever before. If you REALLY dislike the extra partition, then just apply the same policy to all the driver objects as well, that would probably do the trick.