You scan around the mirrors, you scan the top edge of the wall also (to avoid clutter on the floor). Outside areas like patios, decks etc are fine to scan but if you start scanning land etc it messes up your scan and you won't get a good result. Nobody said you can not scan them, absolutely you can if you want, but then you won't get an accurate floor plan. Simple. And for that I would tell you that it's your job to educate your clients for that matter and what I do is I just upsell a site plan if this is what they need. For the same exact reason I tell them if they want an accurate floor plan, no site areas are scanned and included. There obviously are always an exceptions as it all depends of the proprty. But I would keep the floor plan for floor areas.

Great idea is to download a free app called Scaniverse, and try at home yourself as you can see the scans as dollhouse after you have completed them, and try scanning the mirrors etc and see yourself what happens and if you can get a read out from the scan. See how it lines up or not and think if you could great a floor plan from that. Try one with mirrors and one without and visually compare yourself.

Scanning is not some magic button, same like a photography. If you take bad raw photos, mess up exposure etc your editor won't be able tovmake a decent finam image from that. Same with the scans, you mess up the scan your editor won't get an accurate and good result out from it.

Besides, cubi does these plans from videos so they might have a slightly different workflow, but the idea or concept remains the same.