Didn't hear of this until tonight, someone made a tutorial in which he recommends drawing the initial sketch with a red pencil. (which is different from a red colored pencil, he points out)

Then just now I see a FA submission where the sketch is in red, with black traced over. Coincidence?

The tutorial maker's reason for it was that you can trace the sketch properly with a pen (or normal pencil) and remove the red digitally. (by removing colors)

But maybe there are other reasons for using a red pencil? It's like a thing that artists do?
Where to get these anyway,
Have you used them or knew someone who has?