[BrianG]

Yeah, the spark will pit the connectors. Not only does this remove material, but the surrounding area gets sooty and does not conduct as well. Over time and enough arcing, the contact resistance will increase quite a bit - and contact resistance is a bad thing.

Some would argue it's better to just replace the connector every so often instead of using some type of resistor, but I kinda like to make my setups so that they last.