Asphalt used for roofing is sometimes called mastic asphalt. When applied correctly, it can be an excellent and adaptable waterproofing surface. Also, unlike most other roof materials, it can be repaired in-situ by re-heating with a blow-torch and manipulating it back into shape.
It does have a distinct weakness, though, and common failures are seen when it is used on vertical up stands and when the horizontal surface meets a vertical abutment. It will slump when it gets hot in the sunlight and then deform as it cools. This can be seen in the photos shown here. This is a design and installation failure. It is highly likely to crack, blister and allow moisture ingress when these failures occur.
Careful attention to the design detail will avoid these common failures.