I'm new to blender and I've been wondering what the workbench render engine is used for.
As the Introduction says
The Workbench Engine is a render engine optimized for fast rendering during modeling and animation preview. It is not intended to be a render engine that will render final images for a project. Its primary task is to display a scene in the 3D Viewport when it is being worked on.
Workbench is the render engine that displays your scene in the 3D Viewport when you are in "Solid" viewport shading mode. It gives a certain amount of lighting with a small amount of control, especially if you switch to matcap materials.
The idea is to be able to give you enough light to see what your 3d model looks like while being fast enough to support updating the scene in real time as you scroll your view of the scene, or scrub the timeline to see how animations work.