"Why would you want to do this automatically when doing it manually is straightforward enough? The simple answer is that an automated process makes it a lot easier to use multiple operating systems. If you test software on multiple operating system platforms, for example, this ability is especially useful.
"These instructions assume that you have the operating systems already installed and multiple booting using GRUB already configured. GRUB, the GRand Unified Bootloader, loads and transfers control to OS kernel software when a machine starts up..."
