Some artist preferred rub pastel into the texture of the paper and some don't.  When you rub onto paper with multiple colors you created a smooth surface.  Sometime you just need to have each stroke shows.  The reason I choose velour paper for this demo is because you simply cannot mix colors on velour paper.  That's why I think it is a good practice to use this paper for the layering technic. 
Please see the video on youtube for the demo. 
https://youtu.be/1D2XKNy_Qrs