Do you hold onto empty boxes?
Maybe you held onto the box your new toaster came in with plans to toss it after you knew the toaster worked. But that didn't happen. Maybe you've kept shipping boxes because you figured you could use them to store items or to pack donation.
If you’re actively decluttering, then you’ll be filling those boxes with items you'll be donating. However, if you’re holding onto cardboard boxes because you know you’ll use them someday when you get around to decluttering, then you’re allowing bulky items to take up a lot of space.
Empty boxes crowd your space and store only air.