I have tended to hold boxes until the warranty expires, which means I would be less likely to ship that item back.
I do still have my Rythmik box, but they are local to me so I have been considering ditching it, it takes up a lot of space!
If I think I could possibly sell something later, I keep the box. If I know I run it till the wheels fall off, the box goes. The exception would be for something like my Technics SL1200 that I bought BEFORE they stopped the original production run, where having the box adds value (to me, and likely for resell but not really planning to sell it).
The "problem" with breaking down a box and keeping it like that is that usually means you discard the pre-formed styrofoam or other packaging.