Hey there!
Finding the density of an object, such as a cube, can help you identify an object since not every object has the same density. They can also let you know if an object is made up of a pure substance or not.
One real life example would be determining if a piece of jewelry is made purely of gold. Since gold, regardless of shape and/or size has a density of 19.32 grams per cubic centimeter, you can figure out if it is pure gold by dividing its mass by its volume to see if you get 19.32 grams per centimeter.
Hope this helps and have a marvelous day!