Its sort of obvious to most of us that line wight can help clarify, particualrly on high resolution displays and with the new Creo light ground default display. Its the equivalent of bold v plain text.
Just about every CAD package I have used, other than ProE / Creo has had the ability to vary line weights on screen, even my $60 copy of TurboCAD Mac has it.
Just about every technical drawing system in existence uses different line thicknesses for enhanced clarity, technical pens used to be in multiple thicknesses.
Why does PTC, twenty plus years into their CAD development not allow users to alter line weight attributes in sketches?
I put in an enhancement request when it was Proe 2000, lots has moved on, but this hasn't.