One of the most important factors in the overall quality of diamonds is the polish. Depending on the severity of these micro scratches on the diamond's surface, the light that travels through and from the diamond may be misdirected. These small micro scratches can have a subtle effect on the diamond's brilliance or light performance.
Do keep in mind, that since polish has a subtle effect on the overall brilliance or light performance of a diamond, it is recommended that you do not choose a diamond solely on the basis of its polish grade. All essential characteristics of the diamond should be taken into consideration as a whole. If you're looking to maximize sparkle based on budget then focus on higher grades of clarity (grades starting SI1-SI2), cut, symmetry, and polish.