When installing baseboard on an outside corner, over sheetrock, why is it generally better to cut the boards for a miter joint so there's a small gap on the inside of the joint when they're dry-fitted?

Answer - On outside corners, the joint compound generally dips in next to the corrner. By having a gap on the inside of the joint, it allows for the dip, so the joint will look better once the boards are nailed into place.

Installing Baseboard - pages 282 - 298