I'd think the main benefit was independence from Western powers in the French and the Americans. Pretty big deal, even with one million killed from fighting. Maybe one could argue that the war also resulted in stronger government that was able to resist Chinese pressure, which allowed Vietnam to defeat China when they fought in 1979. Vietnam resisted the Japanese, the French and the Americans so it is a stretch to suggest they needed a war to defeat the Chinese as well, but the war did leave Vietnam unified.
There is one line of thinking that the North allowed the Viet Cong to be crushed once