How was the expansion of trade and exploration in the postclassical era important to China during the Song dynasty?

As I know it, in the Song dynasty of China was not reliant on foreign exports as it was self sufficient for the most part. However, many imported goods from the West that the Chinese have never seen was introduced, including weapons, luxury goods and much more. China was also more developed internally than most of Europe and the Middle East, so I'd say merchants from Europe and the Middle East would've benefited more from China than China from them.

However, since marine technology at the time was not sufficient for sea exploration, and so China had to rely on these merchants and tribes that traveled to the far west of China to acquire information and knowledge of the outside world. Technological exchange, cultural and religious exchange and cross breeding was common between the people of Song and Westerners at the time. (more of it happened during the Yuan period, but that's another story) This had been mutually beneficial, and part of the reason why China has a certain number non-Chinese-looking people living in it, and also part of the reason why parts of China practice Islam.

I hope this answer did make sense to you

sources: my knowledge