Query Store is a very useful feature and can help you identify and solve some performance problems, and also learn about your workload and to be more familiar with it.

The main use cases are related to issues caused by changed execution plans. Complex queries can have many potential execution plans and some of them can be performant, while others lead to serious performance problems. The Query Optimizer does a great job when it generates execution plans but sometimes it comes up with a suboptimal plan. It is possible that two totally different execution plans have similar costs. When a complex query has a good plan, it can happen that the next plan for the same query performs badly. And the next plan will be generated when the old plan is not in the cache anymore. This happens when SQL Server is upgrading to a new version, when a cumulative update or a Service Pack is installed, when patching is performed, when a failover happens, and also when a new application or service version is deployed. In all these cases, when a new plan performs badly, Query Store can help, not only for identifying, but also finding a solution or a workaround for, the problem.