In 1963, Indonesia took control of Western New Guinea (formerly a Dutch colony whose status was separated from the rest of Indonesia/Dutch East Indies since 1949), and renamed it West Irian. One curious detail was that Indonesia issued a special currency, the West Irian Rupiah (WIR), which is exchangable 1:1 to the Netherlands New Guinean gulden, and is distinct from the standard Rupiah used in the rest of Indonesia. According to Wikipedia, only in 1971 was the Indonesian rupiah (IDR) introduced in the territory, used alongside the WIR until 1973 when the IDR becomes the only legal tender.
The Wikipedia article says that the New Guinean gulden was a stronger currency than the IDR, and that the IDR was experiencing a high level of inflation. I guess this means the IDR was somewhat undesirable, but I still don't understand the logic of having a different currency in one part of your country, especially when it's a new region that you're trying to integrate. Wouldn't this be an obstacle for commerce with the new territory? If inflation is a concern, wouldn't the WIR still be susceptible to inflation?
From the Indonesian point of view, what was the advantages of having the West Irian rupiah? How would things be much worse if Indonesian rupiah was used immediately? How about the negative effects from having separate currencies?