You can get heated bidets if that's your thing (just mix the hot and cold water pipes), and a rag is to help you dry off afterward.

When I lived in the Philippines and used a bucket and my hand (and yes, alcohol afterward to disinfect), I didn't bother with a rag because it was so hot and I'd dry off quickly anyway. However, in fancier places with bidets, a rag to dry off after is completely normal. And it's just as sanitary as using a hand towel after washing your hands because you're already clean.