Since pressurized growlers are air-tight, you can easily transport beer from one location to another without any loss of quality or quantity. This makes it optimal for whenever you want to take fresh beer or want it delivered to your place of choice.
In many states, breweries can legally fill any growler with their beer, even if someone else's logo is on the container. Basically, any brewery's name on the growler has to correspond to the maker of the beer inside it.