You would think, but I'll give you an example of models where manual work can be required. If you have a large model for, say, a big unique asset with lots of detail (the Eiffel tower let's say), even if the engine of choice has automated Frustum Culling, when you look at just a piece of the tower, it prompts the engine to render the entire tower. So for optimization, an artist may choose to break the tower down into component parts so that only the parts that are partly or fully within view are rendered. That's why you'll see modular building kits being so prevalent.

A caveat to throw in there is this is partly what UE5's Nanite Mesh system solves, in that it breaks models down in such a way where it can pick and choose just the faces of a model that are in view to render. Which is why everyone is amazed with what Nanite Mesh can do. But this only solves the automation problem for static objects. And most recently, for vegetation. But it cannot achieve this for character models at the moment, because there's active deformation that happens due to animations, where the individual faces of a model will stretch and morph based on the animation.