Only drawback: OS X 10.3 cannot be installed on the last partition, otherwise 20GB will be lost. But even under OS X 10.3.3, this last partition can be used for storage etc. So if you have a large hard drive, an older Mac, and the 10.1.5 version of OS X, try formatting the drive there; you may be surprised by the results.
[robg adds: I can't confirm this one as I don't have access to an older Mac with which to test. However, if true, I know a few people who would be quite happy. If someone else tests this, please post your comments.]

