In many case, a single cluster would work extremely well and be very efficient and performant. A very large percentage of the ADX deployments are configured as such.
As Sher wrote, there are scenarios where you would like to separate:
- When different departments use it for different purposes - Operational dashboards and data science
- When ingestion load can vary a lot, a dedicated ingestion cluster (Compute heavy machines) can scale up and down in higher flexibility than a query cluster (Storage optimized)
- When heavy analytics might impact other usages (ingestion dashboarding)
- Scaling out for massive concurrent usage by creating more instances of the follower
Microsoft