Final answer:
The recommended practice for handling shared content between sites is to use a centralized approach by creating a separate module or library.
Step-by-step explanation:
When setting up multiple site structures in the content tree, it is recommended to use a centralized approach for handling shared content. One way to achieve this is by creating a separate module or library for the shared content. This module can then be accessed and used by different sites as needed. By keeping the shared content separate, it becomes easier to manage and update the content without duplicating efforts.