Hmmm.... interesting. I need to let this percolate. Thanks for the input, this is a stimulating discussionI was afraid you were going to make me share my unconfirmed reasoning lol... ok.
When you connect them, you create a loop. From there, I see two problems.
#1- If you cut a loop antenna, its not as good of an antenna any more. So it makes sense to not make a loop.
#2- By doing so you invite any currents acros the frame to pass through the computer ~ allow me to explain. Although it is generally said that electricity takes the shortest path (ground clamp to welding electrode in this example), there can still be issues with that. Consider if your ground clamp is closer to the negative battery terminal and the welder electrode is closer to where the computer bolts up. Whatever the resistance is between those two point, there will be a respective voltage proportional to the welding current. By connecting the positive and negative cables, it can now send a fraction of the current through the computer to get to the ground clamp. If that voltage (due to the welding current and path resistance) is high enough to forward bias anything in the computer, I'm going to let you guess..
Unlikely, yes, given the ground clamp is as close to your weld as possible, but I see absolutely no benefit to connecting those cables.