What does Vacancy Rate expense even cover?

[Schuyler Witt]

This may seem like a very basic question: we are trying to figure out what the set-aside vacancy rate expense that is on the BP calculator and that investors seem to use even covers? Is it solely to cover mortgage payments as long as the property has a loan on it? Or is it to pay yourself so that your cash flow is not interrupted when the property is vacant? Or both? Another way of phrasing it is--do you still set aside a vacancy rate expense once the mortgage/loan is paid off? Thanks for your help! Schuyler