When I first bought my Powerbook (with 6 GB hard drive), I had a great idea. Partition the hard-drive into three sections, one each for MacOS 9, LinuxPPC, and (for the future) OS X (with a few extra utility partitions for Linux swap space, etc.). But then OS X came along, and so did an MP3 collection. I removed Linux, since I could SSH, emacs, and perl perfectly fine in OS X, and the old Linux directory became an MP3 disk. But OS X is huge, and I felt a little cramped in the 1.7 GB partition, and backing up all the data I had would be too difficult, so repartitioning was out of the question. So I wrote Monolingual ( http://homepage.mac.com/jschrier/ ) to remove the unnecessary language resources. But even that was not enough. I saw that there was a swap disk that was taking up a minimum of 80 MB, and more likely 160 MB or more (increasing in size as you use OS X). So why not move it to my MP3 partition (where space wasn't as much an issue), and reclaim the space on my main disk. Thus Swap Cop was born.
Why would you want to do this? Perhaps you are in the same position with an ill-arranged partitioning scheme like I was. Or maybe you have a small disk that you would like to dedicate to swapping, to increase your OS X performance. I originally made the change by hand, but realized that it wouldn't be too hard to have a user friendly program that would take care of it.