The document discusses using Solr as a non-relational data layer. It describes a use case of storing survey response data in Solr documents to enable fast querying, filtering, and faceting across thousands of boolean fields. By leveraging Solr's scalability and query performance, they were able to reduce API response times from 2-15 seconds to a constant 50ms. The document recommends considering Solr when you have frequently read and infrequently written data, need robust search and filtering capabilities, and want a scalable non-relational data layer.