Locking out advance with welds

I'd like to know why welding is such a bad idea.
The first weld cools and shrinks the second does not compensate. Unless you a dial indicator, or listen to the engine tone or use a scope, you will escape the run out that results in timing variation between cylinders. That is ok if do don't mind it pinging on a cylinder or two first. Just back it off some, then the lagging cylinder will lag more. It does not matter if using points or VR sensing.
The other is once boogered with weld, no further adjustment. If welded at top hat slots, still slop in inner shaft to top hat.