MacAppStuff's Pieces is a system utility that lets you split and join files. There are many reasons why you would want to split a file. I have used an application like this in the past to split large files that didn't fit in optical media or were big enough to e-mail.
The upper part of the screen is dedicated to file splitting. Here, you simply select the file that you want to split, and the destination folder. By default, files are saved in the same folder as the source file. The only option that you can change is the size you want to split files into. You can enter it in bytes, kilobytes, megabytes, and gigabytes.
At the bottom, you will find the Join pane. The process is also very simple. All you need to do is find the file that ends with the .001 extension and the application will do the rest. It can even be configured to delete the piece files after the extraction process is completed.
From the Preferences window, you can set whether or not you want the application to notify you when the process is done and how.