Gutters drain the rain by way of an outlet and thru the downspout. The standard outlet would be 3"x4" opening (drain hole) . This size drain hole is normally ok to drain the rain. If you add in a heavy downpour and a large roof or a handful of pine straw or leaves, everything changes. The drain hole in the gutter quickly becomes blocked or clogged. The maxdrain outlet (an extra large drain hole) allows for instant drainage because of the openning 3 1/4" x 8" and allows leaves and pine needles to wash out of gutter, reducing the number of times you need to clean the gutter, maybe avoiding the need for covers. Becareful to filter downspouts that connect underground. See pictures on left