MySQL’s multi-source replication allows a replica server to receive data from multiple source servers. Let’s say you have a replica server at your workplace, and there are multiple source servers in different locations, you need a way to directly receive data from these source servers to your replica server. This is where the multi-source replication technique comes into play. It allows you to efficiently gather data from various sources and consolidate it on your replica server.
Note that this is quite different from merge replication or peer-to-peer replication in SQL Server and there are some limits to its capabilities. That said, I could see this being really useful for performing ELT into a warehouse: use replication to keep the staging tables in sync and then run a job to perform transformations into facts and dimensions periodically.