in 2018.2 it seems to work on very simple drawings. On real plans I always seem to get "Revit will use raster printing because this view uses shading, shadows, point clouds, sketchy lines, depth cueing or gradients.", even when none of these options seem to be used.
I've read that Topography 'triggers' raster printing, not sure why, but switching that off doesn't help either. At the very least that message could be improved upon, or there's a bug that also triggers raster printing for obscure reasons.
Either way, Revit decides it needs to use raster printing. Why doesn't Revit just show what it would look like in vector printing without shading, shadows, point clouds, sketchy lines and gradient?
The warning is ok to the user knows vector printing was selected that might cause differences between the printing and the plan on screen.
Nobody actually wants to search in vain for some element that might or might not be 'triggering' raster printing for some reason, they just want a vector print.
The "offending" elements could be highlighted in the Print Preview. Let the user decide whether he's happy with the vector print or not.