Why partition data?

Improve scalability. When you scale up a single database system, it will eventually reach a physical hardware limit. 

Improve performance. Data access operations on each partition take place over a smaller volume of data. 

Improve security. In some cases, you can separate sensitive and nonsensitive data into different partitions and apply different security controls to the sensitive data.

Provide operational flexibility. Partitioning offers many opportunities for fine-tuning operations, maximizing administrative efficiency, and minimizing cost. 

Match the data store to the pattern of use. Partitioning allows each partition to be deployed on a different type of data store, based on cost and the built-in features that data store offers.

Improve availability. Separating data across multiple servers avoids a single point of failure. If one instance fails, only the data in that partition is unavailable. 

https://learn.microsoft.com/en-us/azure/architecture/best-practices/data-partitioning