The media comes in protective packaging. Once the labels or other media have been removed from its packaging, it will typically pick up dust and particles from work and storage surfaces.
If the media becomes contaminated or dirty, it can damage the printer and cause defects in the printed image (voids, streaks, discoloration, compromise the adhesion of the adhesive, etc.).
During manufacturing, packaging, handling, and storage, the outside length of media may become dirty or contaminated. This will remove any contaminants which might be transferred onto the printhead during normal operation.