It's a set of performance tests built into the Chrome dev tools. It profiles your site on a variety of metrics and gives you a report. I'm not exactly sure what's wrong with it in the context of this post.
I assume the same is true of the other checks Lighthouse does for performance, best practices, etc.
Lighthouse and other such tools are a good starting point, and using them is better than doing nothing, but a thorough understanding of accessibility etc is necessary to create truly accessible and performant sites.