This is one of the most talked about things at the moment, why jailbreak apple TV? Some of the reasons below may answer this question:

• XBMC – XBMC is a Media center originally written for the XBOX, Xbox Media Center was the name, however it has found its way onto other devices such as the Apple TV2, XBMC is modifiable with themes available for download
• NitoTV, lets you play movies in any format, Create playlists, Create or edit network share points, Launcher for applications, settings
• Tweaks

Simply because you can! I will be doing some more in-depth posts on what XBMC and NitoTV are in the following week or so