Using a Revit link as an underlay can be a common workflow for architects and especially for engineers. A link can be set to Halftone to distinguish it from the main model, but new work (model lines, for example) can still end up being obscured by geometry (walls, etc) in the link--making it difficult to see what you've drawn. Revit solves this problem:
The geometry in the link will now be halftone, and more importantly, it's a true underlay: the link geometry will not obscure new lines and edges.