Which of the chessboard appeals more to your eyes?
The left? or the right?
Let's talk about symmetry. And why it's important to have a symmetrical diamond.
To the human eyes we see symmetry as beauty, it captures our eyes, makes things simply, more pleasant to look at.
Take for example, scientists prove that symmetrical faces are what makes most men/women handsome or beautiful / appealing.
But is that all to it? Just looking symmetrical? Maybe I like asymmetrical stuff?
Nope, far more importantly, the symmetry of the diamond, because of it's facet alignment affects the light return of a diamond as well.
Symmetry & Light Return
The above shows 2 AGS ideal 0 diamonds, triple 0's. The one on the right is what vendors these days still call hearts and arrows. It sure looks like hearts and arrows, to someone just starting out, and looking through a hearts and arrows loupe at the diamond on the right will find it symmetrical and fascinating.
However, look at the clefts on the hearts, the uneven lobes, uneven sizes. What does this give you? Broken arrows from the front view? Yes. Also,
Note where i circles the major light leakage under the table of the diamond on the right. Dum dum dum!
Yes, symmetry can affect the brilliance and light return of a diamond because of the way the facets are aligned.
Why does this happen though? Cutters tend to cheat when polishing diamonds, sometimes to save or retain weight on the diamond. And what happens here? We have uneven polished facet surfaces. Which is all revealed in the hearts. A straight polished facet (perfect hearts) allows light to bounce off the facet evenly. Uneven polished facets simply causes light to "slide" off which results in leakage of light. This also means, since light is simply sent in random directions, your diamond will not show a visually balanced firey diamond throughout, instead fire randomly produced, in a smaller effect as well.
Under a white light, your diamond will suffer in brightness, contrast and symmetry patterning.