If you use a block of wire that supports, 4A in the middle of a 5A line, for example, wouldn't it be the only one that would burn in case the line requests 5A?
I'm almost sure that works that way, if this is true, this is the same as a fuse.
Doing it that way seems a waste of resources. People use thin wires whenever it is possible to reduce material costs. That wouldn't really work.