It's easy to file 'low-stock alerts' under minor conveniences rather than real money. Running the actual math on what an out-of-stock popular item costs over a month changes that.
A simple worked example
Say a shop sells a popular item 15 times a day on average, and it runs out unnoticed for 3 days before someone restocks — not an unusual gap without automated tracking. That's 45 missed sales. At even a modest per-unit margin, a few days of stockout on one popular item is a real, countable loss — and most shops running on manual stock checks have more than one item doing this at any given time, they just don't have a number for it.
The second cost: the customer who doesn't come back
A customer who shows up for a specific item and doesn't find it doesn't just represent one lost sale — some fraction of them go to a competitor for that purchase and some portion of those don't fully come back. That cost doesn't show up in any stockout report because there isn't one; it just shows up later as slightly softer foot traffic nobody can explain.
What an alert actually needs to do
Flag an item before it's fully out, not after — a threshold set per item based on how fast it actually sells, not a flat number applied to everything in the shop. A slow-moving item and a fast-moving one shouldn't trigger at the same quantity remaining.
TU2 Market tracks quantity on hand automatically at every sale and flags low stock before you're actually out — turning a cost that was previously invisible into a number you can see and act on.