Here is a quote from one of the developers called devnet.
Unity Linux is a small Linux core based on Mandriva Linux. We whittle down Mandriva to a small base desktop to provide users with ‘just enough graphics’ to be able to login and create their own distribution of Linux with the liveCD project which lies at the heart of Unity Linux
Unity Linux comes with all sorts of desktop versions such as Openbox, Xfce, Gnome, KDE (which is the default choice). In other words, any desktop that is provided by Mandriva will be supported in Unity Linux as well. Although it does lack some packages, but still if you have an internet connection then you can easily install a lot of other applications too.
It has a graphical easy to follow installer, and if you want web browsers or multimedia codes or any other major software for Linux, then you'll have to log into the desktop and install via internet. So then why should you use it?... well, once installed it has a reputation of being fast thus needs little RAM and CPU. So if you have a bit slow PC and looking for something that runs a bit faster then... why not give it a try!.
But remember, if you don't have an internet connection, then you're gonna miss some packages + multimedia codecs,etc.