Under this tab in the brand settings you can choose to preset the banner sizes you usually work with for this brand. Presetting sizes will make it easier for your to access your sizes when creating new banners.
Here you can also add custom scripts that will be applied to all the banner on this brand. This is usually something Bannerflow will help you set up in case you need it.
Under the settings tab you can set up some default behaviour for your banners. You can enter your Banner weight limit and fall back image weight limit so that Bannerflow can show you warnings when you are exceeding the limits. You can also set up the naming convention for your fallback images here.