This extension has 2 major uses.
This is great for doing online arbitrage (OA). The extension calculates the monthly storage fees for the Jan-Oct period and the Nov-Dec period for both the standard and oversize categories. ( You do need to know which category the product falls into, but both are displayed for every product)
This helps you get a better estimate of what your actual profit of the products are slower movers that might stay in the Amazon warehouses for a month or more. This is very important in Q4 when the Nov-Dec fees escalate. This is helpful when deciding how many units to purchase or send in to the warehouse. You may choose to delay sending in large quantities depending on forecasted demand.
You simply click the extension button the Chrome toolbar while on the Amazon sales page and the fees appear in the popup box.
Manually figuring this out would be very time consuming.
The second use for this extension is to figure long term storage ( LTS) fees on products that you might want to remove before having to pay LTS on Feb 15 and Aug 15.
This is great for helping you decide if you should hold, liquidate or recall products.
Once again, manually figuring this out would be very time consuming.