I have read about how China is trying to claim Socotra Rock (a submerged rock 4.6 meters below sea level). However, this is not recognized by international law since the rock is 12 nautical miles from China's territory and is also claimed by South Korea, leading to tension. This tension might make sense if there was strategic value for China to own the rock, but there seems to be no obvious political or economic advantage to owning the location. South Korea only uses the rock for an ocean research station and other than the fact that the rock is tied to an ancient Korean myth, it doesn't give much benefit to South Korea. Why does China want to own this submerged rock so much?
The Chinese government has spent the last decade and more very actively pursuing the extension of their territorial waters into what is commonly accepted to be international waters, or even the territorial waters of other sovereign nations. Mostly within the South China Sea.
They do this by arbitrarily claiming islands, or by creating artificial islands when there are no islands to claim.
The Chinese Communist Party (CCP) then use their economic influence in the region to attempt to pressure smaller or weaker nations into recognizing their claims.
This is an issue they take very seriously. Going as far as to require the printing of the "nine-dash line" (China's unrecognized territorial claim), on all maps printed in China. Companies that operate or do business in China are actively pursued, bullied, or tricked by the CCP into using their maps (which also claim that Taiwan is part of their territory).
While there may be military and political motivations as well, at least one of the primary motivations behind these territorial claims is likely Chinese overfishing. There are huge numbers of Chinese fishing ships regularly aggressively trespassing on the territorial waters of their neighbors.
There are similar issues in the north, with Chinese fishing ships regularly intruding off the coasts of South Korea.
So the Chinese claim to a larger section of the waters between China and South Korea follows the same pattern as their claims in the South China Sea. They want more. If they did hypothetically manage to establish a claim to Socotra Rock, it might allow them to construct another artificial military island to further extend their influence.
Note that the island can emerge from the water at anytime. If it does, it arguably becomes new land to claim, which would allow China to claim land in a strategic location near a neighbour.
Some thing like this occurred a while back on Graham's Island. https://en.wikipedia.org/wiki/Graham_Island_(Mediterranean_Sea)
I agree with Tai, but I am missing something.
What I miss is the strategic component for China. China is land-locked in the South, the West and the North. In addition to this there is Taiwan, Japan, the Philippines and Korea which, in case of conflict, can severely limit free passing of Chinese vessels. Any island or Atol (or submerged rock in this case) that they poses will reduced the chance for China to become isolated. I think this is a very serious consideration from the Chinese government.
The answer provided by Tal would appear to start from the point of view, that China's government are "evil Commies" and can therefore be assumed to harbour all sorts of nasty intentions. So, for the sake of balance, I'll try to see it from another angle.
If you look at a maps of China and the sea territories bordering them, you will see that their access to the Pacific is almost completely walled in by nations that are allied with the US, which means that in the case of a major conflict, it will not be incredibly hard for America to cut off all shipping routes to China. I think it is understandable that the Chinese government is not too happy about this, and therefore seeks to establish some authority in the area.
It is also worth bearing in mind that we in the West have a less that spotfree history when it comes to China; and of course, when it comes to using their economic strength to put pressure on other nations, they have had excellent teachers in the US.
So, to sum it up: having a strong presence, in that area has strategic and political value; and a rock under a bit of water is still a foundation to build a structure on.