A P&L built for your accountant and a P&L useful for marketing decisions aren't the same document, even though they're the same numbers. For marketing purposes, three lines matter more than the rest.
Gross margin, not revenue
Revenue growth that erodes margin isn't really growth. Before celebrating a sales increase, check whether gross margin held, dropped, or improved alongside it.
Customer acquisition cost as a line item
Most small businesses bury ad spend inside general "marketing expense" without connecting it to how many customers it actually produced. Isolate it, and acquisition cost becomes a number you can actually manage.
Contribution margin per channel
Not every revenue dollar costs the same to produce. A channel with lower revenue but higher contribution margin can be more valuable than a bigger one that's barely profitable after fulfillment and ad costs.