You add in 'boot parameters' here, which can cause the system to configure itself in different ways. For example, if the hardware detection fails to identify something correctly you can add a boot parameter to fix things. Also if you have a laptop you may have to put in some info about the display size in pixels.
In knoppix circles they get referred to as 'cheatcodes'. Go to http://www.knoppix.net/docs
and you will see the cheatcodes link near the top of the page.