Catalog's inventory threshold can be used to change the threshold at which Catalog labels your products and variants as “low inventory”. This low inventory buffer can be used to protect or set aside a subset of your inventory and make it unavailable to Partners, thereby preventing overselling.
In Catalog settings navigate to the Shipping, Returns & Inventory tab and you'll see the default threshold is set to 25 units. If you choose to change the low inventory buffer, be sure to check the Mark products as "out of stock" to Partners at this quantity checkbox. Once your variants reach this quantity, Catalog will mark your products out of stock to all Partners.
*For Brands using Shopify, you'll want to be sure that the "Continue selling when out of stock" feature is not enabled on your products