Spring Data Elasticsearch projects are intended to bring in the concepts of Spring Data repositories, enabling easy development of Elasticsearch repositories. They provide an abstraction layer on top of Elasticsearch to successfully store, retrieve, and modify documents available in the Elasticsearch transparently. 

Spring Data Elasticsearch eases CRUD operations by allowing the ElasticsearchRepository interface, which extends from ElasticsearchCrudRepository. This hides the complexities of plain Elasticsearch implementations, which need to be implemented and tested by developers. Using Spring Data Elasticsearch could reduce the development time dramatically because of this. 

In coming chapters, ElasticsearchRepository, with default methods and custom methods, will be used extensively to implement business logic and write and test Spring Data Elasticsearch repositories. The following sections will discuss how to use a domain model designed using a class diagram as a base to implement Spring Data Elasticsearch-based documents and repositories.