devtrackers.gg
You can paraphrase this for lights.
A light or window isn't too much to render on most gaming computers. But as the number increases, the complexity increases exponentially.
If the dev has full control of the scene, then they can add bits of complexity. If the player can add anything and everything, they can add far too much complexity.
Game engines can do some rather impressive stuff with modern GPUs. GPUs and rendering engines still can do far better when the target is the complexity and quality of each frame rather than speed and quantity of frames.
^^^^^^^^^^^^ it isn't straight forward
Glass is deceptively complex for game rendering. Here is an extremely simplified overview of game rendering: Normal objects made of solid shapes are relatively easy to render. Take some geometry, the location of the object, and the location of the camera, you do some linear algebra. Now you know how the object lays on the screen. Last you color each screen pixel based on which part of each object is closest. But how do you color a window or other object with transparency? There are a few ways to handle transparency but I believe Unreal draws the scene without transparency, then it draws the window on top. But what if there is a window on top of that? And on top of that?
Most games avoid this. In most FPS games, for example, only have one window into or out of a room. They avoid level design where layers of glass might overlap on larger portions of the screen because each layer means that part of the screen with have to be redrawn one more time.
However, Satisfactory isn't most games. People can and will make buildings with layers and layers of glass. And every layer of glass will cause the scene to render again. And again. And again. There are ways around this, for example by clamping how many times you can see through glass, but even if that number is 2, you're still redrawing portions of the scene 3 times.
TL;DR: In a creative game like Satisfactory, transparency have significant impacts on your frame rate.
PS: This is over simplified and is mostly just used to demonstrate the complexity of the transparency problem.
^^^^^^^^^^^^ it isn't straight forward