The four-way sort
Every stored item answers one of four ways: KEEP (used yearly — seasonal, heirlooms), SELL (valuable but not yours anymore — the market pays better than the unit), SCAN (paper that hurts to toss but never gets read), or STORE (genuinely needed, temporarily — the between-homes furniture). The sort takes a weekend and typically shrinks the unit a size — a permanent monthly saving.
The monthly arbitrage
Storage costs are a monthly rent on postponement: the $1,200 sofa kept 18 months at $140/month cost more than a new sofa. The arbitrage test — replacement cost vs months × rate — settles most "but I might need it" debates with arithmetic instead of guilt. Items losing the test get sold while they still have value.
The scan-and-release protocol
Paper is the heaviest category by volume and the lightest by value: a fast scanner (or a scanning service) converts boxes of documents into a searchable drive. Tax records: 7 years. Anything else: scan or shred. One weekend of scanning typically eliminates a 5×5 of paper — and the searchable archive beats the box it replaced.