If you formulate queries as SQL string, you have to accept many disadvantages, e.g. not type safe, no refactoring or any other IDE support, non-debuggable, database-specific. However, alternative Java APIs are too complicated for many developers.
With JPA-SQL you are now able to wirte your queries in SQL as you are used to. RapidClipse then generates Javacode based on the JPA Criteria API automatically. Thus JPA-SQL combines the simplicity of SQL with the numerous advantages of the powerful JPA Criteria API, e.g. type safe, fully IDE support, debuggable and database independence.