Snippets define reusable interface parts. They can be used on both pages and layouts. By using snippets you can make changes in fewer places when you modify the interface. For example, you can have a snippet that is used both in the contents area of a template grid and in a data view. If you change something in the snippet, that change will show up in both places.
Building blocks are components that can be re-used to streamline the page creation process. By pre-configuring and styling building blocks, users can easily click together interfaces without having to worry about the details of styling guidelines or user experience.
Building blocks are stored in the app’s UI resources package. This keeps them in sync with the app theme, and provides a handy place to consolidate all design-related data.