why is density such an important physical property?\?

Answer 1

It's useful in some calculations, like whether a material floats or how much a full water tank weighs. It gives clues about the state of matter, whether it's amorphous or what kind of crystalline structure it has. But it's only one property. Others are important, too. A primary one is the number of electrons in the outer shell of the atom, determining its position in the periodic table and governing its behavior in chemical reactions.

Answer 2

Density determines Mass. Mass is used to calculate Energy.