It used the excuse (self-defense) to rescue the murderous Khamer Rouge (spelling) regime and resulted in tens of thousands of death (and more injuried and mis-treated and ignored after the war) of Chinese soldiers (and more Vietnamese deaths). Deng benefited from this in consoidated his power.
If it's such an achievement and victory, why it's almost never celebrated (or even mentioned) since then by the government (similar to another tragedy: June 4).