I just moved and it was really nice to be able to reuse what existing boxes I still had. Many were damaged by a water leak years ago and I had to carefully wrap the loose trains to box.
I'd highly recommend consideration on if you plan to move at some point
I have saved all the engine and car boxes. For me, they don't take up that much room, and I want to be able to repackage them if I sell, trade, have to ship for repair, or move. If I had a huge collection that was on display, I would have to perhaps reconsider keeping some of the car boxes.
I currently have all my boxes for my Locomotives, Rolling Stock, and Accessories. Since in the future I plan on completely redoing my layout, so I am going to need to put them in something when I get around to doing that.
I drew the line with accessory building boxes - they were all discarded after my move from PA to CA three years ago. All other, including engines, rolling stock, power and control are stored away taking up a lot of space in my closets.
