Beyond the fact that it's not healthy for the cars electronics, if you have a voltmeter, you should never have to do this for troubleshooting purposes.
Here's another "old codger" story. When alternators came out in the mid sixties, many of them bit the dust because of people striking the jumper cables together after connecting them to the good battery. They did this in the generator days to see if they had a good connection and a hot battery. (Also it was probably quite fun to make sparks) Then they would connect to the vehicle needing the jump. The diodes didn't like this technique very much.