java jpa spring spring-boot spring-data

What is this property in Spring Boot?

I saw property in Spring Boot documentation for JPA configuration.

  • Is the true default value for this property if it’s not provided at all?;
  • What does this really do? I did not find any good explaining for it;
  • Does it make you use SessionFactory instead of EntityManagerFactory? If yes, how can I tell it to allow me to use EntityManagerFactory instead?