Another thought from one who has learned the hard way;
These brass fittings at designed with soft metal and if a person cranks down on them too hard they can ruin the sealing surfaces and wind up needing to get them re-ground.
Also if the torch valves are hand closed really hard the stem can get bent and that will entail sending it back to the manufacturer to get repaired.
With these precision surfaces the amount of pressure needed to seat the parts gas tight really isn't much more then what is needed to to push the blood out of your skin to a lighter color as you close the parts together.
Seems there is a way that metal to metal contact can actually weld the two parts together and when they are opened again chunks from one surface will get torn out because it is bonded with the other. I think the metal guys call it galling.
I remember that there was an issue with that happening on one of the first space flights when the astronaut (or it could have been a cosmonaut) could not get the hatch closed because of it.
ETA: It's called cold welding and here is a youtube video on the subject;
https://www.youtube.com/watch?v=A8FgA7Narfs