With Optimize Storage, you can automatically free up space on your iMac by making files available on demand. Your oldest files will be stored in iCloud and on your email IMAP or Exchange server, so you can download them at any time. There are also tools to identify and delete big files.
Optimize storage. To see storage recommendations, go to Apple menu Access your iCloud content on your Mac.
Optimize Storage: Save space on your Mac by optimizing the storage of movies and TV shows in the Apple TV app. You can choose to automatically remove movies or TV shows from your iMac after you watch them. You can download them again at any time.
Empty Trash Automatically: Automatically erase items that have been in the Trash for more than 30 days.
Reduce Clutter: Easily identify large files, and delete the files you no longer need. To browse large files, click through the categories in the sidebar—Documents, Applications, Mail, Messages, Books, iCloud Drive, and more.
To help you save space as you work, macOS also:
Prevents you from downloading the same file twice from Safari
Alerts you to remove installer software when you finish installing a new app
Clears logs and caches that are safe to remove when you’re low on storage