Businesses everywhere are looking at their manufacturing processes, and deciding what steps can stay and which are too expensive. During this process, they look at lapping and polishing and think, "why can't I just use the material as-fired?"
Depending upon the substrate, the surface finish, flatness/camber, and parallelism of an as-fired substrate can vary widely. For many applications that require a consistent substrate, this variation is unacceptable. Which is why lapping and polishing are required.
For example, with a thin-film application that requires the use of a photo-resist, the waves, bumps, grooves, and camber of an unprocessed substrate could lead to inconsistent thickness of the photoresist, as well as light diffraction from voids and bumps during development. In this application example, device performance and yields may be greatly impacted by the poor condition of an as-fired substrate.
When your project needs substrates to remain consistent in order to function, lapping and polishing are critical steps that cannot be missed.