Assume for the moment that the chinese had not ended their maritime voyages in 1433.
how might the subsequent development of world history have been different?
what value is there in asking this kind of "what if" or counterfactual question?

I think that the most important point to consider is that China would become the maritime power, and could confront Portugal and Spain as the rulers of the sea. But of course, there are other aspects in this assumption that a general answer. And the value of this question is because make you understand how History works, looking at each subject as a sequence of events. To analyse each event, you have to obtain a previous knowledge about them, and this would allow you to create different possibilities.

Explanation:

Because of the power of their ships, the Chinese fleet was strong enough to control the Indian Ocean and made the trade faster with India than the Iberian countries, establishing itself as a maritime power. Portugal, and subsequently Spain, couldn't confront this influence because, at the end of the 15th century, they were still understanding how to find a way to India (Spain was into a war against the Muslim in its territory). But the failure to overpower China would result in the impossibility to support voyages across the globe and "find" new territories, which would make impossible the conquest of America in the 16th century. Chineses would subsequently be the ones who will find America and colonize it. Soon, the Christian world was not the only one. In a nutshell, it would be a disaster for Europe.