A lens hood can prevent lens flare and light entering the lens at wide angles bouncing off the interior part of the lens barrel which degrades an image.
There are some practical points to consider. If it is a case of shooting in scenic areas where there are few or no people around, then it may be advantageous to simply put your lens hood on a wide angle or telephoto zoom and get out of your car and shoot.
The disadvantage in some areas and some countries is that placing a substantial lens hood on a telephoto lens connected to a DSLR brings you a considerable amount of visual attention that is not always wanted, particularly if it is from pickpockets, beggers, muggers, and tough looking guys who do not like photographers or tourists. I was once threatened by a guy with a machete. Not using a lens hood enables you to easily keep your camera out-of-sight in your case and only bring it out when you are ready to shoot.
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