Branch microservice design pattern is a design pattern in which you can simultaneously process the requests and responses from two or more independent microservices.
So, unlike the chained design pattern, the request is not passed in a sequence, but the request is passed to two or more mutually exclusive microservices chains.
This design pattern extends the Aggregator design pattern and provides the flexibility to produce responses from multiple chains or single chain.
For example, if you consider an e-commerce application, then you may need to retrieve data from multiple sources and this data could be a collaborated output of data from various services.
So, you can use the branch pattern, to retrieve data from multiple sources.