CIPS and CNAPS are not alternatives
They do different halves of the same payment, and the confusion is understandable because both were built under the People's Bank of China and both have "payment system" in the name.
- CIPS clears renminbi across the border. Its participants are banks.
- CNAPS routes a payment inside mainland China, to a named branch. Its identifier is the twelve-digit code a supplier gives you.
A CNY payment from Hong Kong to a Shenzhen factory generally uses both: CIPS to bring the renminbi in, CNAPS to put it in the right branch. Being told your bank "uses CIPS" answers a different question from the one an invoice asks.
What a buyer actually does with it
Nothing, and that is the useful part of knowing what it is.
CIPS participation is your bank's arrangement, not a field on a payment instruction. There is no CIPS code for you to collect from a supplier, nothing to type, and no step you can take to make a payment "go via CIPS" — your bank's correspondent arrangements decide that. What a buyer supplies is the beneficiary's name, account number, SWIFT/BIC and, on a CNY leg, the CNAPS code.
Where it does show up is in explanations of why a payment took the route it did, or why a bank quotes different times for CNY against USD. Worth recognising; not worth chasing.
Why it keeps coming up anyway
Two reasons, and both are about somebody else's incentives.
Banks and payment providers describe CIPS access as a feature, because for them it is one — direct participation is faster and cheaper than clearing through a correspondent. That is a real difference in their costs, and only sometimes in your price.
And "cross-border renminbi" is the phrase attached to the question most importers are actually asking, which is whether to pay in CNY at all. That question is about the conversion, the paperwork and who bears the exchange risk, and the clearing system is the least interesting part of it.