The Pagespeed Insights Checker tool is important because it helps website owners and developers identify areas of improvement in the performance and loading speed of their websites. This tool analyzes a website's code and content and provides recommendations for optimizing images, reducing the size of files, and minimizing the use of third-party scripts. By implementing these recommendations, website owners can improve the user experience for their visitors, increase conversion rates, and boost search engine rankings. Additionally, the tool also provides a score that indicates the website's overall performance and loading speed, which can be used as a benchmark for future optimization efforts.