This depends on the application.
If the rendering distance is larger, more objects have to be managed by the CPU. For example Minecraft, there you have "chunks" that store the block information of an area of 16x16x256 blocks. When you move, new "chunks" come into the view area, so the CPU has to load or generate them.
In other games, new objects (geometry) must be loaded from disk and sent to the GPU. Modern games have so many textures and models that the GPU is not able to store them all. So the CPU has to decide which textures and models are needed.
Other aspects can also play a role. For example, animals walking around. As long as you are too far away to see them, they don't need to be updated. But if the rendering distance is greater, they should move.
More rendering calls also play a role. However, not as strongly as the aspects mentioned above. Because in general, the number of different geometries that need to be rendered should not be too large. And with instance rendering, objects with the same geometry can be rendered multiple times with just one drawing call.
Does a high draw distance always imply high CPU usage, or is something that could be optimized, but sometimes isn't?
No. The render distance is part of the projection matrix. When comparing two render calls:
- Entire scenario is in range:
- Entire scenario is in range, but render distance is doubled:
The rendering time will be the same.
Even with drawing calls for each geometry in the world, both renderings will take the same amount of time (on CPU). On GPU, of course, things look different...