A boot tray acts as a low cost humidifier when filled with water.
Water evaporates slowly from the boot tray and mixes with the air
raising the humidity level. The large surface area of the boot tray allows for faster water evaporation. Placing them near a heat source like a furnace heat vent or radiator will increase the amount of evaporation.
Increasing room humidity helps soothe dry noses and throats while reducing static electricity.
Mine is located under the bed. It’s out of the way there.
Natural evaporation is better than a humidifier that use electricity and filters.Humidifiers can breed mold or bacteria if not properly used or maintained. Boot trays only need a quick rinse in the shower when empty to remove minerals left by evaporation. I go thru 1 gallon of water every 3-4 days. That’s 1 quart of water going into the air every day in one room.