3. Typically, an IO and a PO from the same trust can be recombined to form the underlying collateral for a 1/32nd fee and resold as collateral. While this typically never happens in practice, it creates an arbitrage floor for the IO and PO prices, which is important from a liquidity and pricing standpoint. This is much harder to do for floaters and inverse floaters, as both sides of the combination in that case may be harder to find and less liquid, not trading on broker screens as Trust IOs and POs do.