When I sell my 5 year old flagship phone I'll get $30 more easily if I have the box and the stuff that came in it. People see that and subconsciously think "this person has their shit together. buying their used phone isn't a risk."

Same goes for other stuff, too. I recently sold a synthesizer for $150 over the market rate because I had the box, manual (even though it was out of date due to firmware updates) and the stickers that came with it.

I like semi up-to-the-minute tech, so keeping things in good shape and giving someone the unboxing experience keeps my costs down at the cost of a little space in my closet.