I am curious as to what the benefits of a cargo freight station are, as I built one and it has helped spark traffic on my previously deserted residential freeway.
Many Industrial and commercial buildings produce goods, receive goods, or both. Each one of those deliveries is represented by a cargo truck you see driving along your roads. They are either traveling between two buildings, leaving your city or entering your city from outside the map.
When your city grows, then you will soon notice that all those trucks start to clog your road network, causing all kinds of problems.
Using cargo buildings (cargo train terminal, cargo harbor or cargo airport available in the Industry DLC) gives your cargo trucks alternative routes to travel through your city, into your city or out of your city. Trucks entering your city can alternatively arrive by train, ship or plane and enter your road network from the cargo buildings instead of the edge of the map. Trucks leaving your city might travel to the nearest cargo building instead of traveling all the way out of your city by road. A truck traveling to a facility on the other side of your city might take a shortcut by traveling by road to cargo building A, using its transportation method to travel to cargo building B, and driving by road from cargo building B to its destination.
So some well-placed cargo buildings can be a great way to solve road congestion problems.
But on the other hand, a badly placed cargo building can cause havoc to your traffic planning by attracting a lot of trucks to areas which aren't designed to handle them. So make sure you place cargo buildings in (or close to) industrial quarters which receive or send out a lot of freight trucks and that your cargo buildings have a generous road connection to those quarters and to the rest of your road network.
Build a cargo train terminal to allow trains to carry goods and raw materials. Cargo trains can operate inside the city or with an outside connection. Build stations and connect them with tracks before using the train line tool to make a line.
Building it within your city might be good to transport goods to other places in your city. The Outside Connection will help your city get goods from other places. Source: https://skylines.fandom.com/wiki/Cargo_train_terminal