Cloud storage is a wonderful way to extend limited hard disk or SSD space on your computer to an accessible internet-reachable location. Many services combine synchronization and storage offloading. Synchronization ensures that files on every linked device are stored in a central repository and copied and get up to date on every attached device. Storage offloading lets you opt to keep the file in central storage but not on every end point after the file is first uploaded.
Dropbox and iCloud Drive are two popular options for macOS, iOS, and iPadOS cloud storage, and they differ substantially in this approach. Dropbox changed its approach last summer for personal accounts, so it might be a little different than you recall if you haven't used it for a while.
