Major Description
In some cases the GAV is only there because Maven expects it, even though these coordinates will never be used.
The most common case is an aggregator: it will only trigger module without being part of a multimodule project.
Another case I'm thinking of are test-cases, where you want to show the behavior of some plugins. This project self will (or should!) never be installed or deployed.
In general: the GAV is only required when another project will refer to it or if you want to distribute the project via a M2-repository manager.