This is a fast way to set the Maximum Quantity for your product(s). When you enter the Maximum Order Quantity it will update your Seller Central (Amazon) automatically within 2 to 5 minutes of you exiting the field.
This feature is useful if you have special deals and want to limit the number of items that can be purchased in a single order.
Note that if you make changes to the Title field that will also push to Seller Central, so be careful when editing.