SAP HANA XS Advance and UI5

I would like to clear my confusion regarding the development track of SAP HANA XS Advance and UI5. What is the difference between them.

In my understanding through XS Advance you can build any application.Why would anyone need UI5 with HANA XS Advance in the same way if anyone deveoping its application in UI5 then there will be no need of development in HANA XS Advance.

In my understanding HANA XS Advance only useful when you need scalability.

Please anyone clear my understanding.