It is important the water runoff pours into the eaves, thus it is recommended that the shingles are installed with a drip edge.

The edge of a roof should lengthen beyond the fascia board, approximately 3/4 of an inch.

If this slight overhang is too short, water will drip behind the gutters, leading to rotted roof sheathing and fascia, stained siding, and even soil erosion and a flooded basement