Certain special vaults like the PUSD stability pool vault utilized an external contract to hold and convert "special" payments that the normal vault code does not account for, such as MATIC payments from Polyquity's stability pool after a liquidation. During a large downward price movement, the PUSD stability pool vault received over 900k MATIC worth of liquidation payments, which required the developer to withdraw it to an external contract and convert it to PUSD over the course of multiple days in order to avoid getting "rekt" by slippage.