Directional tread patterns have increased water channeling ability (anti aquaplaning) and water clearance is its main advantage over all other tread designs.
As the tyre rolls forward it channels water forward and diagonally out to the side of the tyre which keeps the water from building up under the tyre which would cause aquaplaining.
Directional tyres are easily identified by its V shaped tread pattern, because the tyre channels water in a certain direction running the tyre in the reverse direction to what its designed to will channel water into the tyres contact to the road area resulting in aquaplaining.