Windows 10 Storage Sense uses the cloud to free up disk space

The upcoming Windows 10 feature update will deprecate the Disk Cleanup tool in favor of the more advanced Storage Sense. The latter will run automatically to optimize your disk space by removing temporary and unnecessary files, and will be able to work in conjunction with OneDrive cloud storage to save even more disk space, by removing local copies of OneDrive files that aren't frequently used:

The next update will perform some of this management automatically. As part of its 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 determine 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 perform its duty periodically (daily, weekly, or monthly), or automatically whenever your disk is low on space.

Via: ARS Technica