The rental value of the property determines the margin that creditors will extend to you. If your property value dropped (with last paid rent being the proxy f

The rental value of the property determines the margin that creditors will extend to you. If your property value dropped (with last paid rent being the proxy for this), you'd be liable to be margin called. If you're fully vested on margin in something illiquid like real estate, then it very well might be better to have a few vacant properties than be forced to liquidate to cover your margin balance. Obviously though this has the makings of a real estate bomb, as a few forced liquidations could set off a cascade of value collapses.