Citus users typically have a working set of a few hundred GB or more and run into memory and CPU limitations on a single machine on both the write and the read side.

Provided your data has a natural sharding dimension (e.g. tenant ID in a multi-tenant application), Citus can distribute tables across many servers to scale out memory, CPU and storage. It can also parallelise queries, index creation, aggregations, and deletion across the cluster, and it can horizontally scale out write throughput. This gives you the necessary tools to deal with very large data volumes.

e.g. 500k writes/sec https://www.citusdata.com/blog/2016/09/22/announcing-citus-m...