By default, macOS can free up space by removing the local copy of files you downloaded (they remain in Basecamp, just return to their "cloud" state). If you want a file or folder to be always available, even without a connection, you can pin it.
Always Keep on Device
- Right-click the file or folder in Finder.
- Choose Always Keep on Device.
The local copy is kept and not automatically removed.
Free Up Space
- Right-click the file or folder.
- Choose Remove Download.
The file returns to its "cloud" state and frees up space. It remains in Basecamp; it will be re-downloaded when you open it.
Note: Removing the download never deletes anything from Basecamp, only the copy on your Mac.