To prepare the business case to get this work done, this may be the first thing that you have to do. You can only do it if you have a list of what is in the boxes.
Imagine that you have 144,000 files in 7,500 boxes. Each year it costs $6 to store one box or $45,000.
You realise that that you can destroy 60% and transfer 40% to Archives. Annual savings of $45,000. Makes sense to process it