The PIF provides the literal foundation (no pun intended) for your asset protection structure. The PIF is controlled by you. The IBC is controlled by the PIF.
Only the IBC can conduct business, but without the PIF as part of the structure, you would end up with direct control of the IBC. This would give you “interest in a foreign corporation”, which the IRS can use in order to assess taxes to you. With the PIF as shareholder, you can honestly say (and the public record will confirm) that you do not have an interest in any foreign corporation.
Additionally, the PIF can be used to provide for you and your family. It can own property, hold or invest money, own precious metals, etc. You can instruct the PIF to send regular stipends to your favorite relatives, or provide for your family after you die. The PIF structure is unbreakable.
The IBC can conduct business anywhere in the world. Between the PIF and IBC, you can do almost anything while retaining both privacy and control.