I think a lens hood is critical when the camera is pointed in the direction of s strong light source, or when there's a bright field of light and a dark field subject...I think the lens hood, also called a lens shade, can be a critical accessory in many situations. Now, some lenses flare or ghost pretty badly when shot right toward the light.
One tip: the Nikon 70-200mm VR lens, the first generation model, flared badly when shot toward the light. When shooting sunsets, or shots at twilight, I found that the Mamiya R-system's rubber lens shade for the 360mm lens was perfect for pressing inward with my fingers, to literally bend the shade down a bit, and thus throwing a literal shadow onto the front element.
When you need the absolute-best from a lens, a good lens shade is necessary to make sure you get all the contrast the lens can deliver. That's why compendium lens shades still exist, for demanding still and cinematography uses.