The WireTap Studio Library.wtpl file contains all of your recordings and edits. This file is located in your Documents folder by default. This file can get rather large after while, but you can easily relocate it to another location, such as an external drive.
To move your library to a different location, simply quit WireTap Studio and move the WireTap Studio Library file to your desired location. When you launch WireTap Studio again, click the Choose Library button and navigate to its new home and you should be all set.
Holding down the option key while launching WireTap Studio will bring up the same window with library options. This is helpful if you wish to create or utilize multiple libraries.