Tim is right. I was talking about "rehoming" of caravans and freights, which is of benefit if you can rehome to a city with more trade arrows than its creator city. Some players of lore used to refer to a Super Trade City rather than a Super Science City, where everything was done to maximize the number of trade arrows, and Copernicus and Newtons were an afterthought (or even unnecessary). Deliveries to and from that monster STC are so valuable that you can lower your Science rate to emphasize Taxes or Luxuries instead (for more WeLoveTheConsul/PresidentDays, or to pile up gold for city improvements). A couple GOTMs have started with Fundy government, which halves city science across the board, so relying on caravan/freight deliveries bypasses the drop in city research.
There is a trick where you can create a one-way Trade Route to a STC without disturbing its existing routes to other/AI cities: lower your source city's trade arrows to a couple below the size of the smallest existing TR cities' population size just before delivery. Most AI cities have roughly the same number of trade arrows as it's population. If yours is slightly less, the TRs in the STC will not be disturbed and you will create a one-way TR from your source city to your STC.