There's all sorts of scenarios involving Taiwan where Chinese carriers would come in useful in sealing off the Western Pacific.
For one, suppose the US believes that it can still successfully resupply Taiwan in a conventional war, because it has more carriers and can push forward from Guam. Control of the waters beyond the 2nd island chain means the US Navy could perform a maritime blockade of China.
On the other hand, if China has a larger blue-water carrier fleet, then it is the Chinese Navy which has the ability to control the sea lanes and ensure global trade continues.
China needs a larger carrier fleet to successfully deter the US from intervening with Taiwan.
If China has a smaller fleet, it's not enough of a deterrent as the US could believe it can win a conventional war.
Who has sea-control is also part of the calculation that smaller countries will make in deciding where they stand between China and the USA.
I doubt China is worried about US all that much in the western Pacific. 003 and 004 are aimed at Taiwan, not at US.