Yoga is not only a work with physical body, it´s a spiritual practice.
Practicing on a clean rug is part of Sauca – cleanliness.
My teacher said: You have to love your practice, not being too attached, but take care of it and everything what is coming along with it.
Rug is easier to clean that the mat. Mat is almost impossible to wash.
Rug is like a bed sheet – when you need, you was them. You do not wash the entire bed (mat).
If you are sweating more, keep rotating 2 rugs so you can wash them often and prevent that sweat will set in.
You can think - micro-fiber ‘‘yoga‘‘ towel might do a same thing, right? But washing them often might be a issue for the planet.
You can read more about how materials are affecting us and our yoga practice here.