paying the mortgage. If you put the money into your primary residence you own a property with no income stream. If you put the money in property that produces income you have an alternative source of income that can pay the mortgage.
$400,000 put into a home builds equity and eliminates 3.5% interest expense.
$400,000 put into income producing real estate builds equity and provides a revenue stream. If the revenue stream is the same size of your mortgage the risks are the same but now you are building twice the equity. The revenue stream of the property in this case can pay for your mortgage in a crisis.