Nothing!
Except that you did not leverage. But leverage has cost and of course, the risks.
Only if one can access the market/assets at it bottoming out or on the way rising, then it may make some sense.
If not, the risk is the leverage will also erase your capital twice as quick. (has not the housing bubble taugh us a lesson? if yes, why do we continue debate this issue?)
Yeah, one can say if it has cash flow, just keep it. Eventually the price will rise. But rise on what? Rise on worthless USD?
Of course, one can say zero down will have infinite return. The presumption is that cash flow will always be positive for the duration of the loan or forever, who can guarantee that, especially in this economic environment? someone can, I can not. :)
In reality, when housing finally bottoms out, it will be the great time to buy real estate with cash (or better yet with precious metal), because interest rate will be at record high then. (Do not beat me up, I read somewhere that in Weimar Germany hyperinflation peak, 1 oz of gold could buy a section of street - maybe just like someone said and 5 oz gold in early 1900 can buy a 四合院 in Peking). :)
