A perpetual inventory system promises a stock figure that is always current. That promise is real, and it is the reason most growing operations move to one. But the real-time number is not free, and the costs are easy to underestimate before you live with them.
The ledger drifts from reality
The recorded quantity only stays accurate if every movement is captured. In practice some are not: a unit walks out unbooked, a return sits in a corner for a week, a scan reads the wrong SKU. None of these throw an error. The book quantity simply diverges from the shelf, and you keep trusting it until a count proves you should not have.
It demands operating discipline
Perpetual accuracy is an operations habit, not a software feature. Receiving has to book stock before it moves. Picking has to confirm what left. Adjustments have to be entered the same day. A team that treats these as optional will run a perpetual system that is perpetually wrong.
It does not remove counting
The most common misconception is that real-time tracking ends physical counts. It does not. It changes them from a full annual stop-the-line event to ongoing cycle counts that reconcile the book to the shelf. That is usually a better way to count, but it is still counting, and it is still work.
So when is it worth it?
When the cost of being wrong is high: tight margins, fast turns, automated reordering, or customer promises made against available stock. If your volume is low and a stockout is cheap, a periodic system may cost you less to run and lose you little. The decision is about the economics of your operation, not about which system is more modern.