Allowing multiple Gerrit servers to trigger the same build job would reduce the number of total build jobs if the build pipeline to be executed would be the same.

Real world example: In our company two departments have separate Gerrit servers that use the same CI build pipeline to verify commits. The pipeline script makes use of the exposed GERRIT_* environment variables to clone the code, so it is "Gerrit server agnostic". However, I still need to have two separate build jobs because I can only select one Gerrit server for triggering the build.