Hoya is main brand.
Kenko is the same actually.
Filter protect the lens from dusty industrial photography situations, sandy hands from drunks at the beach, like zoukout, pyrotechnic sparks flying into your lens, wedding guests spraying champagne into the cam... Bird or bat droppings at highly popullated caves or sanctuaries. Pets or creatures which likes to lick. Kitchen oily smoke in restaurants. Children party throwing chocolate cakes around. Paintball shooting and splattering right on the lens. Saltwater sea sprays or crashing waves splashings. For a busy photog on the go shooting from assignment to assignment, point to point, there is no time to sit down under the light and slowly clean. It is easier to just unscrew the dirtied filter put on a clean one and worry about cleaning later.
The people who say you don't need filters are often portrait photogrs shooting in prefered conditions.
Filters are not for impact protection, a hood does better.