(I'll preface all of this with saying I'm new to creating flat file uploads)
tl;dr - We're a FBM seller. I tested the "Inventory Always Available" option on a product. It updated the inventory count to -1. Is that correct or am I missing something important?

While trying to learn how to upload/update products using Amazon's listing templates, I noticed this option to enable "Inventory Always Available" on products. This could be extremely useful for us since we manufacture safety signs that could be shipped out immediately. I did a test on one product and the only change I noticed was that it updated the test products inventory count from 100 to -1. I changed it back to 100 immediately after because having it set to -1 just seemed wrong, but I can't find anything that talks about this option, so for all I know maybe I should have just kept it at -1.
I researched the FAQ, forums, articles, youtube videos, anything that could give me insight on what I should be expecting when setting up a product with this option, but I'm coming up with nothing.
I've also reached out to support to see if they can give me any amount of information, and even provided a screenshot of this option from the spreadsheet, but I was brushed off quickly and told that "there isn't a direct "inventory always available" option. Sellers are responsible for managing their own inventory, ensuring products are available for sale and that stock levels are accurate".
Does anyone have any experience with how this option works and if I'm doing something wrong?
Thank you!