What is the purpose of the go_package_prefix in the buf build library?

Question

I I don't understand the purpose of the go_package_prefix code snippet in generating protobuf files

version: v1
managed:
  enabled: true
  go_package_prefix:
    default: github.com/imsobad/grpc-gateway-demo
    except:
      - buf.build/googleapis/googleapis
plugins:
  - plugin: buf.build/protocolbuffers/go:v1.30.0
    out: gen/go
    opt:
      - paths=source_relative
  - plugin: buf.build/grpc/go:v1.3.0
    out: gen/go
    opt:
      - paths=source_relative
      - require_unimplemented_servers=false
  - plugin: grpc-gateway
    out: gen/go
    opt:
      - paths=source_relative
      - generate_unbound_methods=true

I want to understand how the command "go_package_prefix" work