system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the point in ever having trains run between platforms at subway stations?

As someone who frequently uses the subway, I find it odd that not all stations follow the pattern of train platform train, where the platform is in between the trains so that you can access both trains going in both directions from the same platform. 

Instead, there are stations that follow the pattern of platform train train platform, so you can only access one train going in one direction from each platform, and to go in the other direction you'd have to get to the other platform, usually via stairs.

I don't see the benefit in ever constructing a station like the second example. In fact I distinctly remember not being able to find how to get to the other platform at a certain station and having to take the train in the wrong direction to go to a different station where I could then change directions.
gpt
It's to reduce congestion so you don't have everyone that wants to go North and everyone that wants to go South in the same area. It also reduces confusion if you pay attention as the trains only access the platforms from their right so you know which direction they are heading.