Listing Settings are essential to list on eBay and are strongly recommended for Amazon and other marketplaces. 

They are templates that allow you to have custom settings for different groups of your products and allow you to control a number of  variables including Price and Stock, plus for eBay they allow you to control your shipping, listing duration and other options.

Some customers find that they only need to create one Listing Setting per marketplace, but having the ability to set up multiple templates makes for great flexibility.

Click on the logo below for a tutorial on the relevant marketplace.