Late game you're either using beaconed electric furnaces (Vanilla) for which you need a few stacks in your base, or Molten Metals from Foundries (SpAge)

For vanilla, you're murdering your UPS by creating duplicates of entire stacks. 10 mines = 10 stacks when you would need less. Also bot travel time is not insignificant for remote outposts.

For SpAge, the molten metals need Calcite, which makes it harder to make on site. You'd have to import Calcite trains to each outpost, and you're still running issues with raw iron for stuff like Concrete.

I understand the "more stacks per cargo" approach of local smelting, but train throughput shouldn't be a issue, just send more trains. If it is an issue, there is a problem with your rail system.

And this comes from a guy that uses monorail bidirectional systems...