According to Ars Technica,the October edition refresh will use OneDrive cloud storage.  Windows 10 currently uses placeholder files to make OneDrive cloud storage better. With placeholders, the local OneDrive directory appears to contain the full directory structure and all the files that are found in the cloud.  If you try to open or modify one of those files causes the data to be retrieved from the cloud.

As part of Vole's Storage Sense feature, Windows will be able to automatically remove the local copies of OneDrive files, unless they've been set as always available offline.

The operating system will work out which files to remove based on when they were opened: files used more recently than a certain number of days will be retained locally, while those that haven't been used will be replaced with placeholders.

The system will remove files until the operating system reckons it has enough free space for normal operation.

Storage Sense can remove temporary or otherwise unneeded files such as system logs and image thumbnails. It will remove old files from the download directory.

The temporary-file cleanup - which can also remove certain cache files, driver packages, old anti-virus definitions, and more - was previously handled by the Disk Cleanup tool.

Storage Sense can perform its cleanup process periodically or automatically whenever the system is low on disk space.