when would you want to use the 'rebook dates' function?

When BRM creates a rental ticket it automatically updates the calendar of each and every item of inventory in that rental, automatically.
Meaning those items are 'IN' that rental and can't be double-booked, so you don't need to worry.
But there is a menu option called 'reBook dates'.
under the admin menu in the reservation detail panel:

So, why might you want to use this technical feature?
only if things get messed up. Imagine, for example, you update your fleet, changing some product lines etc. You will get a warning that some dates are no longer booked, then you can visit that reservation and 'rebook dates' to ensure that all dates are consistent with your new inventory.