The Performance Efficiency pillar of the AWS Well-Architected Framework is primarily concerned with the ability of a system to adapt to changes in load by provisioning resources efficiently to meet system requirements. The pillar focuses on using computing resources efficiently to maintain efficient performance as business needs evolve. It does include considerations like low latency and high throughput but is not solely focused on them, as it also encompasses selecting the right resources and maintaining efficiency as technology evolves. The emphasis on 'primarily focuses' is incorrect because this pillar has a broader scope.