Soldering onto the ground bus is quite tricky due to the thickness of the wire. Even with my relatively decent soldering iron, it involves heating the joint for 3-4 seconds to get it to the right temperature, which is greater than the ideal two second maximum for a joint.
For a more technical explanation of relative thermal mass, here's 80s American Soddering Guy:
I'm not worried about heating bus wire or any of the teflon wires attaching to the ground bus, but I really didn't want to overheat the vintage mustard cap that connects directly to the bus. The solution is to use a crocodile clip as a heatsink:
The croc clip conducts all the heat away from the cap and removes any chance of overheating. Simple, cheap and effective.