Non-photo/reproducible isn't as elusive as it used to be. It can be printed and scanned just fine, however, you can still get rid of it using the hue/saturation adjuster in photoshop if you like.
Most artist that sketch in color just prefer the visual separation it provides. I'll usually sketch in blue, but as I refine what I'm working on I'll switch to red (or green on occasion). Then when I'm inking, I find it easier to tell the black inked lines from color lines than I would lighter gray lines.