@thomthom said:
I can't see, at the moment, any use of adding a pattern to line edges.
I think the difference between patterns and using a lighter edge color are subtle. However, there may be times when they can be useful.
Here is a sample of the steps from this white house, using normal (thin) edge lines (upper left) and making them light grey in SketchUp (upper right), 50% mask and 50% transparency (lower left) and 50% mask, 75% transparency (lower right).
The images are extracted as a detail from a larger model at the top and then blown up 4X at the bottom so you can see how the transparency and masking works.
http://wiki.renderplus.com/images/2/26/WH-detail.JPG
I have put some larger examples on the RPS Wiki
Here is the whole image with 50% masking and 75% transparency:
http://wiki.renderplus.com/images/2/25/WH-small-4.jpg
And the same image with light grey edge lines in SketchUp
http://wiki.renderplus.com/images/e/eb/WH-small-2.jpg
Again, the difference are subtle, but there may be uses for them.