What does exploding a viewport do

Exploding a viewport essentially creates a 2d drawing of the viewport contents, which can then be edited. So one can quite readily clean up prints, thicken lines or darken lines, etc. The viewport no longer reflects the drawing and will no longer be updated with model space changes.
In order to explode a viewport, it is necessary to uncheck both Renderable Objects and Non-renderable Objects boxes under the Properties/Render/Hidden line (or whatever format)dialog for the Viewport.