A good example of this is the image below. The trees on the left and right feature only the limbs you can actually see from the perspective of the camera. The tree in the middle represents a lot more branching. If we’re only concerned with the perspective of the camera, the trees on the left and right are probably more appropriate – a ton less vertexes.
If we need to be able to walk it, then the tree in the middle is likely to get even busier as I find attachment points for the leaves.