starter kill relay

Could someone please tell me the reason why a diode is installed in a starter kill relay and is it necessary to install the diode. Thank You

When energizing the coil of a relay, polarity of the coil does not matter unless there is a diode across the coil. If a diode is not present, you may attach positive voltage to either terminal of the coil and negative voltage to the other, otherwise you must connect positive to the side of the coil that the cathode side (side with stripe) of the diode is connected and negative to side of the coil that the anode side of the diode is connected. Diodes are most often used across the coil to provide a path for current when the current path to the relay is interrupted (i.e. switched off, coil no longer energized). This allows the coil field to collapse without the voltage spike that would otherwise be generated. The diode protects switch or relay contacts and other circuits that may be sensitive to voltage spikes. (JimR, contributor, install bay member)

Thank You for the excellent information.  My next question adter reading your post is what are we protecting using a diode form a voltage spike in a starter kill realy.  Doesn't that wire go to the starter coil? 

The diode protects switch or relay contacts and other circuits that may be sensitive to voltage spikes.

The info I posted came directly from this website. https://www.the12volt.com/relays/relays.asp Maybe you may want to give feedback to have them change their information.