I have all plot styles in my .stb set to "Use object lineweight". My plot styles are Normal (prints object in on-screen color), Black (forces object to print in black, regardless of on-screen color), Monochrome (print object in greyscale-version of on-screen color). and three different shades of grey. (prints object in shade of grey, regardless of on-screen color) Object lineweight is NOT controlled in the .stb. I find this makes things work much better.
This lets you do things like XREF in a "reference" drawing, and set all XREF layers to print in the "Light Grey" plot style. If the other layers in the drawing are in the "Black" plot style, this will make objects in your current drawing print in Black, and the objects in the XREF print in light grey. The XREF is "greyed-out", but all lines keep their relative lineweights. This makes the XREF look like a de-emphasized part of the drawing - it still looks "right", just greyed-out. If you set your lineweights in the plot style, you can't do things like this.