The Apple Extended Keyboard is similar in layout. If you use your computer for word processing, surfing the Web, sending e-mail and other simple office automation tasks, these keys are the equivalent of the human appendix. No doubt useful once, their real purpose is lost in the mists of the distant evolutionary past, but they are still with us because no one has ever bothered to get rid of them. In others, it will exit the program. Mostly these days, it doesn't do anything.
Some programs still use it as a way of capturing a screen image to save as a file.
This key once kept the screen from scrolling, but most applications ignore it. This key calls a quick halt to the action, and it still works. Move the cursor to the top of the page, hit a down arrow so the cursor starts sliding down the screen. Many games respond to this key. The latest innovations in keyboard design separate the keys into two groups and change the angle of the keyboard.