Loan vs all cash purchase

[Michael Win]

I know people purchase properties with all cash.  Can someone explain to me why anyone purchase a property with all cash rather than finance it.  I just bought 6 duplexes  and here are the numbers for the two options.

Total price 1 mil.

If I purchased it for 1 mil, the free cash flow would be $85k (these are hard numbers from 2014). ROI would be 8.5%

I financed it with 30% down. so for 300k, the free cash flow for 2014 would be $85k-42K (P&I) = $43k. So my ROI would be 14.3%. If you account only the interest portion (30K), my free cash flow would be $85k-30k = $55k or a ROI of 18.3%. I consider the principal payment portion income which makes complete sense to me.

So paying cash, my ROI is 8.5%. I would also deplete my cash that could be used for other investments, security, rainy day fund, etc.

By financing, my ROI is 14.3% but effectively $18.3%. I would have more cash on the sideline to finance other non real estate ventures (which I am looking at), buy more properties, etc.

What am i missing?  What are the advantages of buying a property outright other than the peace of mind?