[Gunner]

Originally Posted by IndyCobra

Actually, voltage spikes (the perceived need for the diode) are mostly a figment of the imagination.

It might seem so in auto/aero electric circuits. They're certainly real when driving relays with electronic components - I've seen many a transistor or IC power output damaged by driving a relay without a protection diode. I suspect they're just as real in vehicles but there are no components sensitive enough to be affected by them. It becomes a "might as well" sort of protection under those conditions, probably never serving any purpose. As they don't cost anything (maybe a buck, for a new, high-power diode) and can't hurt... "might as well."