When you want to use lighting that differs from the scene main light to make character face more clear or to add shadows that look ideal. But, in HDRP, one directional light cast shadows, not more than two. The Box Light provides the solution for this. The Unity Toon Shader now supports the feature. For now, HDRP Ray-traced shadows isn't ready for this feature.
Box light applied to a character's face. Note that editing the angle of the box changes the shadows falling on the face, but not on the body and the ground.