The quietest lever of all, because it needs no transaction, no deal, no shipment. Just a revised opinion.
Depreciation requires management to estimate each asset's useful life. The coffee shop's $50,000 espresso machine over ten years costs $5,000 a year. But who says ten? One day management "reassesses" and concludes the machine will actually serve fifteen years. The yearly charge instantly falls from $5,000 to about $3,333, and profit rises $1,667 a year, every year, with no change in the machine, the coffee, or the cash. Scale that logic across an airline's fleet or a telecom's network and revised lives can swing profits by hundreds of millions.
Sometimes the revision is honest, machines genuinely do last longer than old assumptions. The tell is direction and timing: estimates that only ever get revised in the profit-flattering direction, or that get revised in years when the company is straining to hit targets. The revision is disclosed, but in the fine print of the notes to the financial statements, which almost nobody reads.
How a reader spots it: D&A shrinking as a share of revenue with no matching change in the business, and, for the diligent, the depreciation note in the annual report stating the assumed asset lives. Compare them to last year's report and to competitors. A company depreciating identical equipment over twenty years while rivals use twelve is telling you something.