This is a Dehumidifier. Its main function is to reduce excess moisture/water vapor in indoor air.
Simply put:
Extracts moisture from the air and turns it into water.
That water collects in the lower tank.
Reduces dampness in the room.
Helps reduce the risk of mold/fungus and bad odor on walls, clothes, furniture, etc.
Helps a bit with drying clothes.
Especially useful during the rainy season or in closed, damp rooms.