Yes, the weld limits mechanical advance. In the second photo you can see the tip of the weight contacts the cam close to the center axis. The weight can't get enough leverage to continue advancing the timing. The vise keeps the weight cool so it doesn't soften or damage the bushing while welding. The tip is soft and will eventually wear away but this car won't see enough hours for that to be a problem.
As I'm sure you have observed, I don't always do things the same way others do.
