That means that when we use the proportion of the distribution we have passed through to evaluate the match between two distributions (i.e., we use a pp-plot), we will get a lot of resolution in the center of the distributions, but less at the tails. On the other hand, when we use the quantiles to evaluate the match between two distributions (i.e., we use a qq-plot), we will get very good resolution at the tails, but less in the center. (Because data analysts are typically more concerned about the tails of a distribution, which will have more effect on inference for example, qq-plots are much more common than pp-plots.)