Why is Tawang in Arunachal Pradesh important to China?

The PLA transgression in Yangtze plateau is an annual affair, since the PLA intruded into Somdorong Chu in 1986-87, as a part of Chinese plan to show that the territory is disputed. Just like the then Indian Army Chief Gen K Sundarji launched a counter to Somdorong Chu without even informing the then government, the Indian Army this time too was prepared for the PLA and repelled them.