Just cleaned out mt garage, closet, and attic. No clue why I kept every single box of anything electronic/tech based in the last ten years. I just tossed boxes for phones I haven't had in years, old CPU and heat sync boxes, boxes for 100mbps nics, old modems I don't have anymore. I've never needed any of these and have brought them with me through too many house moves.
This is the big reason. I keep the boxes to make future moves easy, learned the lesson the hard way.
Other good reasons are the box keeps all the accessories in one place while saying what they are for (psu boxes, looking at you) or the box is great at storing that type of item, like the box my NAS drives came in, perfect foam insert for other drives