People need a certain level of humidity to be comfortable. In the winter, indoor humidity can be extremely low, and the lack of humidity can dry out your skin and mucous membranes. Low humidity also makes the air feel colder than it actually is. Dry air can also dry out the wood in the walls and floors of our houses. As the drying wood shrinks, it can cause creaks in floors and cracks in drywall and plaster. Dry air also increases static electricity.
It can maintain a certain level of humidity for plants and pets in your home.