Why do hotels always have sheets on the bed? Many people don't know what they're used for

INGREDIENTS:
1 liter whole milk
1 cup sugar
4 large eggs
1 tablespoon vanilla extract
½ cup sugar (for caramel)
STEP BY STEP PREPARATION:
MAKING CARAMEL:
Place 1/2 cup sugar in a saucepan over medium heat. Stir until sugar is melted and golden brown. Quickly pour into the bottom of the pan and spread evenly before it hardens.
CAKE MIXTURE:
In a large bowl, beat eggs and sugar until smooth. Gradually add milk and vanilla. Mix gently until smooth.
BAKING IN A BOILER:
Pour mixture over caramel in pan. Place pan on a baking sheet lined with hot water and bake at 180°C for 50 minutes or until a toothpick comes out clean.
COOL AND SERVE:
Let cool completely, then refrigerate for a few hours. Carefully unmold and enjoy this sweet and nostalgic treat.