Canon Lens Hood ET-54B For EFM 55-200mm IS STM
What good is the hood? The primary use for a lens hood is to prevent light from hitting the front lens element from the sides – reducing contrast and creating flare. Pictures taken with a lens hood installed can have richer colors and deeper saturation.
A secondary use for a lens hood is to protect the lens. The damage prevented can range from a finger-printed front element (a minor inconvenience) to a broken front element (possibly a major expense – and lost pictures/downtime). Lens hoods are generally strong and stick out from the lens some distance. Accidental touches and scratches to the front element are reduced simply because the glass is more difficult to reach with the hood in place. Some impact protection is gained from having a sacrificial part taking the blow. Of course, ultra wide angle lenses have very short hoods that offer very little protection.
Lens hoods on longer focal length lenses offer more front lens element protection from rain and dust. Of course, if your lens is not weather sealed, you should not let it get wet in the first place. A clean and dry front element will allow the camera to deliver the better image quality you expect.