A Custom Feed is a feed template that is unique to your account. Settings and requirements are specified by the user. GoDataFeed does not maintain these feeds so it is up to you to ensure the quality of your Custom Feeds.
When you create a Custom Feed, you are actually creating a feed template that will be available for use throughout your whole account, across all your stores. This is especially useful if you manage multiple stores' feeds and need to implement unique feeds for various channels. It's also very useful when you want to customize your Google feeds, i.e., Google Jewelry Template, Google Apparel Templates, etc.
The new Custom Feed template will automatically become active in the current store at the instance of creation.