a) You can ask your trading partners to trade with you in your own currency, which eliminates currency risk for your companies. E.g. an American company can just sell their stuff for a fixed USD price, and their trading partners will have to take (or hedge) the risk of their currencies fluctuating against the USD.
b) You will have lower borrowing costs for your government debt. If your currency is a reserve currency, that means that many foreign central banks will hold your currency as currency reserves. And they won't stash cash in their cellars, they will buy your government debt (e.g. Treasuries). More people buying your debt means lower borrowing costs (and thus interest payments) for your government.
c) If you control a currency that is used for international transactions, this gives you extra-terrestial legal leverage over the parties of these transactions. The U.S., for example, uses its "ownership" of the USD to enforce their sanctions regime and other laws: many banks e.g. in Europe will not process your payments to Cuba (particularly not in USD!), even though there are no European sanctions against Cuba, just because they can't afford to lose access to USD clearing in the US and thus don't want to risk antagonizing the US.
d) You can borrow internationally in your own currency. This is not an important thing for China, which has huge reserves, but it will be for other countries. If people don't trust your currency, you will have to borrow in USD or another foreign currency. This means your country can go bankrupt: If you are running out of USD / EUR / etc. you can't service your debt anymore. If you borrow in your own currency, you cannot really go bankrupt: you can always just print more money to service your debt (this will have negative effects such as inflation, of course, but it might be less catastrophic than a default).
I think one of the major benefits is, when china’s currency is accepted by other countries, that means the products (or service) made in china are accepted by other countries. When chinese products are accepted by other countries, those countries are willing to use their own products to trade with those chinese products...
I am not talking about specific products, but those manufacturing in macro sense...
There is no use to hold a certain currency when you are not able to use it for the time being or at some point of time in the future...and the more you hold a certain currency, the longer you are expecting it is useable or the more you expect it to increase its value.
a) You can ask your trading partners to trade with you in your own currency, which eliminates currency risk for your companies. E.g. an American company can just sell their stuff for a fixed USD price, and their trading partners will have to take (or hedge) the risk of their currencies fluctuating against the USD.
b) You will have lower borrowing costs for your government debt. If your currency is a reserve currency, that means that many foreign central banks will hold your currency as currency reserves. And they won't stash cash in their cellars, they will buy your government debt (e.g. Treasuries). More people buying your debt means lower borrowing costs (and thus interest payments) for your government.
c) If you control a currency that is used for international transactions, this gives you extra-terrestial legal leverage over the parties of these transactions. The U.S., for example, uses its "ownership" of the USD to enforce their sanctions regime and other laws: many banks e.g. in Europe will not process your payments to Cuba (particularly not in USD!), even though there are no European sanctions against Cuba, just because they can't afford to lose access to USD clearing in the US and thus don't want to risk antagonizing the US.
d) You can borrow internationally in your own currency. This is not an important thing for China, which has huge reserves, but it will be for other countries. If people don't trust your currency, you will have to borrow in USD or another foreign currency. This means your country can go bankrupt: If you are running out of USD / EUR / etc. you can't service your debt anymore. If you borrow in your own currency, you cannot really go bankrupt: you can always just print more money to service your debt (this will have negative effects such as inflation, of course, but it might be less catastrophic than a default).