Here you will find information on what an HID relay harness is used for and when you want to install one with your HID Kit. HID Auto Vision recommends a relay for EVERY HID Kit installation but it is NOT required for 90% of vehicles. A relay harness will allow for more longevity out of your HID Kit because it helps provide a more consistent flow of power to the kit thus allowing for less fluctuations in power which in turn creates less wear on internal ballast components.
Here you will find information on the key differences between HID Headlights compared to Halogen headlights. This article clearly lays out the benefits of HID over halogen.
HID, High Intensity Discharge, (also known as Xenon) refers to lighting technology that relies on an electrical charge to ignite xenon gas in sealed bulbs, similar to the lightning phenomenon in the sky. HID lighting does not have a filament but instead creates light by igniting an electrical discharge between two electrodes in an air tight tiny quartz capsule filled with xenon gas. HID lighting are also called Xenon lighting, referring to the gas inside the HID bulbs.