I’ve built distributed applications for years. Put in simplistic terms, you break down an application and data into parts that run on the platforms that will provide the best performance and reliability.
Back in the day, we deployed applications on smaller hardware platforms, such as x86-based servers. We needed distribution. By using distributed processing, we could scale to greater processing loads and set up active/active failover systems where one system could instantly back up the other in the case of an outage.