Scratches are a form of permanent damage. Depending on how deep the scratch is, it can affect your drawing experience. For more examples of surface wear and how to minimize it go here: Surface wear on pen tablets.
Below is an example of some scratches that while ugly, do not interfere with the drawing experience. Small scratches are also hard to see sometime and greatly affected by the lighting conditions.
As you can see the scratches can be very small. These kinds of scratches will not affect your drawing experience.
Here is a close up view through a microscope:
Deeper and larger scratches are also possible. This can definitely affect your drawing experience.
Dropping sharp objects onto the surface of a pen tablet can result in big changes. The crater below was formed by an accidental dropping of scissors from a height of about 6" above the pen tablet.
