Does the Paper Serve a Purpose?
Yes, although its role is fairly simple.
The sheet of paper acts as a clean surface between the sink and the glass while helping to cover the drain opening more completely.
It can also absorb small amounts of condensation
and create a tighter seal beneath the glass.
Some people use paper towels instead of regular paper, while others prefer reusable silicone mats for the same purpose.
Why Place a Glass Upside Down?
The inverted glass helps trap air over the drain opening.
By reducing airflow, it becomes slightly more difficult for odors from the plumbing system to enter the room.
It also prevents insects from easily accessing the drain opening if they happen to travel through the plumbing system.
