This detail changes the cabin end wall into a false front. It's a great place to hang your shingle and might work well for a for a home office or workshop.
It can fit in nicely with other buildings in a homestead compound and start to turn the place into a real little town. Build another one as a future guest house and tie them together with boardwalks.
Construction details for modifying the cabin in this way is now included in the Little House Plans kit.