Stationery, packaging, brochures, loyalty cards, leaflets...
There are aspects to printing that can only be learned from experience. How colours will behave on matt or gloss stock. What small type will do when combined with large blocks of solid colour on the same page. How text reversed out of an image will reproduce. The amount of shifting that goes on within a print run that might make a border uneven when it's guillotined or die cut. What's involved in creating a cutting forme with proper tolerances to produce a box or counter display that will be robust yet easy to fold and assemble...