Fixtures in ERPNext and the Frappe Framework is a tool to help export Data and Settings. When you need to have data migrated to your custom apps, fixtures will come in handy to help you achieve this.
A simple bench export-fixtures command creates a .json file with the information you want to migrate. This information can then be imported to the other application by running the bench migrate command.
Custom fields are also a way to add your custom fields to doctypes created by ERPNext, and ensure your fields will not get erased the next time you upgrade the instance.
