Have you ever tried to use an application such as a game, video editor or photo editor that requires the use of F1-F12? Pressing FN and the F1-F12 key each time can be irritating, with FNSwitch you can easily disable the need to use the FN key. Now you're done with your application, uh oh, the volume key is making a ding noise. Time to use FNSwitch again, now your volume button works.
FNSwitch has two different applications included in the bundle to ensure maximum compatibility with OSX