Question on Cash on Cash Calculation

[Steffany Boldrini]

My mentor taught me to calculate the CoC with the interest only payments of the loan (not principal reduction). Now a friend of mine said it should include principal part of the payments on the CoC. Since commercial loans can be 20 or 25 yrs fully amortized, how is this a fair calculation? What would be a good CoC return for you? Should we indeed include the principal payment on the CoC calculation? Please only respond if you're 100% sure how this calculation is made, I've searched online and there's no clear answer. Thanks!