Every address in CAF has a delivery point ID. In BS7666 parlance this is known as the UPRN. The delivery point ID of an address does not change from one version to the next.
If your client system does not have any need to submit updates to CAF (i.e. because it can be safely assumed that all addresses you need will already be present and correct in CAF) then it may be sufficient for your system to store only the delivery point ID for each address, and not the CAF ID.
This call is provided to give such systems a means to retrieve the current version of the address.