This is one of LEGO's smaller attempts to make a mini-modular floor & window dressing system work consistently across multiple builds & sets, and it doesn't work out to be much more useful than it was in the larger sets.  Basically the display window and door can be swapped to the sides, or the whole thing can be mostly mirrored left to right if you want.  The two alternate builds abandon the system altogether, with good results.

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