Shading with directional lines helps
describe the contour and volume of an object.
On a larger compositional level, your choices often depend on the
feeling you want to create,
like suggesting atmosphere or action etc...
In the picture below
(No.1) this technique is called
shading along the axis or shading along.
I use this type of shading in my work the most
(No.2) Is called bracelet shading. The lines are
going around the axis.
This one gives the image a three-dimensional look