The data_enhanced plugin is the x-pack counterpart to the src/plguins/data plugin.
It exists to provide services, or parts of services, which
enhance existing functionality from src/plugins/data.
Currently, the data_enhanced plugin doesn't return any APIs which you can
consume directly, however it is possible that you are indirectly relying on the
enhanced functionality that it provides via the data plugin from src/.
Here is the functionality it adds:
Search sessions are handy when you want to enable a user to run something asynchronously (for example, a dashboard over a long period of time), and then quickly restore the results at a later time. The Search Service transparently fetches results from the .async-search index, instead of running each request again.