Many Odoo customizations can be made directly from the user interface.
This has the advantage of being a rather quick way to make changes to applications. It can be used from small modifications, such as adding a field, to larger customizations, such as creating an app with several models, views, and menu items.
These customizations done directly from the user interface have some limitations, when compared to customizations done with programming tools, covered throughout the rest of this book. For example, you can't add or extend ORM methods (although Automated Actions can be used as a close alternative to that). They also can't be easily integrated into a structured development workflow, such as running automated tests ...