Hello 👋,please asides from storing costumers data in a non sendable data extension does a non sendable data extension has any other use?

Hello Ngala, 

Broadly speaking, you are right. No other use case apart from storing data which can be vital in audience segmentation and targeted email sends. 

Sometimes, you don't want to show your internal data to customer which is used by you to create your market audience. 

That's the only major use case. Just to add, all major AMPScript and Lookup functions, automations are build on non-sendable data extensions to generate audience related data which can later me used for targeted email sends.

Thanks !