Store in iCloud selects iCloud Photos and Optimize Mac Storage.

In Photos, choose Photos > Preferences, then click iCloud.Store in iCloud turns on the Desktop & Documents Folders and Optimize Mac Storage settings. In macOS Mojave or earlier, choose Apple menu > System Preferences, click iCloud, then click Options next to iCloud Drive.

To turn off iCloud Drive entirely, deselect iCloud Drive. Then click Options next to iCloud Drive: Store in iCloud turns on the Desktop & Documents Folders setting. If you're using macOS Catalina, choose Apple menu  > System Preferences, click Apple ID, then select iCloud in the sidebar: Store in iCloud turns on the Optimize Mac Storage setting on the right.You can also control those settings directly within each app. The button for each recommendation in the Storage Management window affects one or more settings in other apps. A powerful disk analysis tool for MAC Disk Analyzer Pro is a powerful tool which provides you a detailed overview of which files and folders are hogging the most disk space on the system, grouped by file size, file type, file date and other attributes.How to Keep a Mac's Hard Drive Clean: Jun 21, 2016: en: Forbes: This Old iMac Finale: How To Supercharge Your Mac: May 12, 2016: en: Cult of Mac: Spring clean your Mac with these awesome apps: May 4, 2016: en: OSXDaily: 3 of the Best Disk Space Analyzers for Mac OS X: May 1, 2016: en: DigitalDojos: Top 5 Mac Productivity Apps: Mar 24, 2016: en.And also some apps store files, back-ups, etc, in a non-transparent way. If you work with a lot of large files (audio, video, graphics), play games, save photos, it's easy to chew through HDD space. It's worth paying the $10 this software costs, since it's so fast and intuitive that it will make hard-drive organising painless.

Files that you’ve used recently remain on your Mac, along with optimized versions of your photos. Each file stays right where you last saved it, and downloads when you open it. When storage space is needed, files, photos, movies, email attachments, and other files that you seldom use are stored in iCloud automatically. Optimized Storage in macOS Sierra and later* can save space by storing your content in iCloud and making it available on demand.

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