It lets you add switched accessories easily. Usually people either wire directly to the battery and run the risk of leaving them (e.g. heated grips) on when they leave the bike, which flattens the battery, or people have to splice into the loom and make their own switched wiring. This does it for you without having to cut into the loom, and has a relay to reduce the load on the stock wiring.
It's a bargain at £30 for a plug and play switched accessory connector with individual fuses.
Edit: mine run, LED spotlights, heated grips, heated jacket, and two cigarette sockets for providing Sat Nav and dashcam power.