I was hung up on materials that could be printed in 3D.
I can think of two 2D applications:
1) Elmer's glue for precise definition of a design that uses glitter.
2) Woodworkers' glue ... Titebond, etc. for precise location and amount on delicate projects.
There may be many applications in 2D that can be printed on something other than our build platform. Foamcore, plywood, model railroad parts, RC models, Moderate-volume production of an assembly ...