Assuming that you mean Linux, the benefits are very simple. The OS isn't as bulky as Windows and is virtually virus fee there is no need to fear spyware and you get the chance to run free and open source software without giving Microsoft money or breaking the law by running a pirate version of Windows.
Check out gOS it looks pretty good or run Ubuntu. If you are wanting something really slim though try Slackware. There are tons of distros to choose from, just go online and find what suits your needs, if this isn't a production machine use it to learn Linux and soon you will find yourself opening up the terminal window more on your Mac.