Darknets have multiple uses. These can be used to host flow collectors, backscatter detectors, packet sniffers, and IDS boxes. The elegance of the Darknet is that it cuts down considerably on the false positives for any device or technology.
The goals of the Darknet are simple - to increase awareness, and to ease mitigation. With a Darknet in place, it is far easier to determine the amount of naughty traffic on a network, as well as the sources of said traffic