Spreadsheets are great until they're not. When you're updating stock in one tab, invoicing from another, and copying numbers by hand, you're one paste error away from a wrong quote or an oversell.

Switch when you notice: stock and invoices are out of sync more than once a week, you're spending more than a few minutes a day on stock updates, or someone else needs to see or edit the same data and you're sending files around. That's when dedicated inventory and billing software pays off. Stock updates flow into invoices and reports; no double entry.

Pick something that works offline and on your phone, not just on a single laptop. You want to check stock and send an invoice from the shop floor, not from a desk.