It has to do with the company's balance sheet - their list of assets which they use to borrow money. If they have 1000 units that they say are worth $1 million

It has to do with the company's balance sheet - their list of assets which they use to borrow money. If they have 1000 units that they say are worth $1 million each, they can borrow from banks as if they are sitting on $1 billion of assets. If they sell one of those units at $500K, they now look like they have $500 million, which not only impedes their future borrowing but can trigger obligations to their current lenders.