It's there to let you do the ultimate repair. Restore your PC to the way it was when it came out of the box.
It contains everything to set the PC up again. Windows and all the device drivers, all the OEM's utilities, and any bundled extras.
It probably has an option to let you burn the contents to a set of CD/DVDs as an alternative recovery medium, but be very sure that what you burn is bootable and complete before you decide to delete the partition to regain the space.