For non-super-selective schools, differences in GPA and test scores can be associated with different yield rates. When UC had UC StatFinder publicly visible, it showed that yield rates were inversely correlated to admitted applicant GPA and test scores. The reasons should be obvious in that those with higher GPA and test scores have more attractive alternatives to choose from.
For super-selective schools, GPA and test scores may not be much of a differentiator between applicants, though it is possible that some other evaluation of the subjectively graded aspects of the application could be used in estimating yield chance for an individual applicant.