A client has three different sites with three locales.

In Salesforce Commerce Cloud, a shared library is used to manage content assets that can be accessed across multiple sites. This setup is particularly useful in multi-site configurations where certain content, like media files, branded content, or general information, needs to be consistent across different sites. The shared library allows for central management of these assets, reducing duplication and ensuring consistency. It does not, however, typically handle content slots or locale-specific content directly; those are usually managed at the site or locale level to cater to specific market or regional needs.