You could probably use this to shade fur in lined art too, but I mostly use this for painted artwork.
Some clarifications;
1.) For fur, usually simple designs work the best. If you're worried about markings getting lost, you can go back and apply them using a filter. (Ex; multiply for dark stripes, overlay for subtle designs, add for white/light markings.)
2.) I add the shadows in using another layer set to multiply (around 70% - 40%, depending on the piece), then combine the two to blend them together to make for a smoother, more natural appearance. If I'm not using a background, I tend to use a dark magenta to shade, because I think it looks dramatic. If I do, I pick the darkest background color and use that.
3.) Fur is made up of lots of different hairs, so I like to repeat the last step again, but with a smaller brush. It helps add contrast and really make the character feel more lifelike.
4.) Highlights! I use a small brush for this bit, and use lots of curving strokes that follow the shadows I've already laid out, with bigger brush strokes used on the outsides of each clump of fur. I also do this bit on a separate layer set to add (40% - 25%), then combine it with the main one. I also use this time to add little bits of fur sticking out of the ends to make it seem a little more real.
Hopefully this helps out a little! I might do a couple more lol.





