Precision cut gems are far superior to native cut gems. Native cut gems are produced to maximize carat weight, giving little regard to proportions, optics and light transmission of different materials from which gems are cut. Native cut gemstones are often moderately to severely windowed (some even have French doors!) and have poor symmetry which defeats the whole purpose of owning gemstones: sparkle!
Great care and much time goes into making precision cut gems. Tremendous amount of work is put into making a symmetrical, light reflecting beacon optimized to gather as much light as possible in a tiny form factor - and shine it back at the observer. The result is sparkles upon sparkles, and ultimately a very happy gem owner.