It was more a matter of common enemies. The main targets of German aggression would be great Britain, France, Eastern Europe, and the Soviet union, primarily in the European and African theaters. The main targets of Japanese aggression would be Britain, France, China, and the United States in the Asian and Pacific theaters. Neither country had any territory that the other one particularly coveted.

So what did either country gain out of the alliance? This would be somewhat debatable. The British forces that the Japanese were fighting were largely naval units and colonial forces. It is unclear exactly how much service these would have been in the European theater. American forces were divided, however the Pacific war was largely a naval one, and the U.S. Navy was largely not needed to fight surface actions against the Germans. Although manpower was divided, it wasn't exactly short in either theater for the Americans.

The one thing that Germany wanted most out of Japan was for the Japanese to open up a second front in the far east against the Soviet union. However, the Japanese had fought a largely secret and mostly losing military action against the Soviets in the years leading up to the war. They wanted no part of war with the Soviets, and the Soviets were more than happy to oblige them with the huge German army pouring in. This truce was rather strictly obeyed until the waning days of the war, when the USSR declared war on the Japanese well after things had become a foregone conclusion.