Seriously... I might as well just be using an ordinary text editor and a command line compiler.
But..but...that wouldn't require you to have the latest version of OS X (since XCode 4 is now distributed through the AppStore and dropped support for the 10.5 API), would leave you with over 4GB more of hard drive space (what's the point in having all that space if you're not going to use it?), and not require you to re-download the full installer every time there was a point upgrade!
Why would you ever want THAT?