The six main drivers for granularity disintegration are as follows:

Service scope and function

Is the service doing too many unrelated things?

Code volatility

Are changes isolated to only one part of the service?

Scalability and throughput

Do parts of the service need to scale differently?

Fault tolerance

Are there errors that cause critical functions to fail within the service?

Security

Do some parts of the service need higher security levels than others?

Extensibility

Is the service always expanding to add new contexts?

https://developersummit.com/session/granularity-communication-for-microservice-architectures