The most overlooked benefit is the lens hood makes the lens longer and sexier.
Lens hoods also look sexy. You get more looks from the bewildered crowd around you!!!
As per negatives. I would say they are expensive. Canon does not include lens hoods with their non-L series lenses, which is pretty cheap of them.
Also, as mentionned above, lens hoods get in the way of filters and other devices that you may want to attach in the front of the lens.



Clients won't take your serious.are there any negatives to using a hood