you should always have a unit not leased so that you can lease it to someone who needs it now and is willing to pay. If you only have a few units though you will never hit that point where the theory is worth the risk the desperite person comes along.
Why would that desperate person be willing to pay the xN premium needed to cover the idle time?
Why would there be exactly one desperate person in the market? You need a curve, charging more as the space fills up. Desperate renters don't have infinite money. People with money are the people who are not desperate, because they have flexible options.
