Ledger boards make it easier to fit and hang inset doors.

This supports the doors while I'm dialing in the gaps around them (with a series of trim cuts), and does the same when I am transferring hinge locations from the cabinet to the door. To make it less awkward to hang inset doors, I lay the cabinet on its back and use double-sided tape to attach temporary ledger boards just inside the opening. [Extracted from the article]