YugabyteDB's automatic sharding and declarative partitioning enable developers to scale their databases without losing performance or flexibility. By defining primary keys and secondary indexes, users can optimize their schema for various use cases, including data distribution, clustering, and geo-distribution. This approach allows for a wide range of scaling possibilities, including the ability to limit the number of declarative partitions for lifecycle management or data placement. With automatic sharding and declarative partitioning, developers can create optimized schemas that balance distribution and clustering to achieve high performance and scalability in their applications.