Wave Linked Geometry is used for assembly processes. For example, if you have to components you want to assemble and in the assembly state, you want to drill a hole in both components. So, you can add the two components in an assembly, Wave Link those two components and then add holes in both Wave Linked bodies. Then, you can create an assembly drawing with your components having the holes in them. But, yet, the components you brought in the assembly will still have none of these holes.
Wave Link Geometry basically gives the ability to add features to the assembly that should not be in the component file. Manufacturing Engineers use Wave Link Geometry to help their work on finished components.
Also, some companies do not like 2D drawings in the same file as the model, so they put the Wave Linked Geometry in the 2D drawing file and draft from there. This is good for concurrent or parallel work, you have the designer working on the model at the same time the drafter can do rough drafting at the same time.
So, Wave Linked Geometry can be used for multiple purposes.