when a broker dealer or market maker has to purchase shares because there are not enough buyers it is known as eating stock 
if there is more demand for an ipo than there is supply creating a shortage a higher price can be charged for the securities resulting in more capital raised for the issuer which also means more fees earned for the underwriter however oversubscribed ipo shares are often underpriced to some extent to allow for a post ipo pop and robust trading to continue to generate excitement around the issue companies leave a bit of capital on the table but may still please the internal stockholders by giving them a paper gain even if they are stuck in a lock up period benefits and costs of oversubscribed securities