I tend to think if an item has a box, it may be better cared for, and may be complete.
Right or wrong, I presume the owner may have been more meticulous about the item.
More accurately, I assume folks who discard boxes use the item roughly, especially regarding storage and overall care.
For me, it will be easier to store and protect when not in use.
Unboxed items on ebay are items I skip, unless very rare or meant for a bash.