The principal benefits of a two tier structure (i.e., a Qualified Opportunity Fund (QOF) investing in a Qualified Opportunity Zone Business (QOZB) over a QOF-only structure are that (i) Qualified Opportunity Zone Business property needs to account for only 70% of a QOZB's total tangible assets (as opposed to 90% of total assets in a QOF-only structure), (ii) a QOZB can use the 31-month work capital safe harbor but a QOF cannot and (iii) if a later investor that already has funded a QOF wants to invest, then that QOF can invest in the QOZB (which would not be possible in a QOF-only structure, because one QOF cannot invest in another).