You have a bunch of structured data you’d like to search; you’d use query language, correct? What if you have a bunch of structured data you’d like to expose to customers to search? You wouldn’t want them to use SQL as the interface. You’d want a search tool. AWS CloudSearch is the beginning of the tools you want to use.
Search is complicated, from managing the application to scaling the backend. The search infrastructure may grow more complex than the database holding the data. AWS CloudSearch aims to reduce that level of complexity by offering it as a service. While not as robust as Google or Bing, I can see extending the functionality to take data dumped in S3 buckets, transformed, and searched using CloudSearch. Well worth the deep dive.