Question for fighters or trainers...

We've seen a few times during the season when the fighters are trying to make weight by sweating out excess water in the sauna. I get that part... but we see them removing the sweat from their skin using a card such as a driver's license or credit car like an ice scraper.

The first time I saw it, I just assumed it was a matter of convenience. But they made a point of showing it again later in another episode.

What is up with that? Why don't they just use a towel to wipe themselves down? Is there some arcane knowledge at work here?