Not entirely true.
Several times aIready I have been glad having kept them when I had to return devices because of warranty stuff.
So it makes sense to keep the boxes for half a year or so.
Real problem is, in reality I still have smartphone boxes dating from 2005 lying around which I am just too damn lazy to sort out... ๐
That's interesting, because the boxes of my work phones are the only ones I throw away immediately.
Why should I care to return the phone to my employer in a fitting box?