Whatever data I have backed up in the cloud is synced across multiple devices that I use. Even if the cloud disappeared altogether, I still have it. The cloud allows me to keep an up to date copy across various devices.
Both Google Drive/Photos and OneDrive have an option to only keep recently used files on your local device, and even periodically suggest they automatically remove local copies of unused files to "free up space".
I highly suggest everyone disable this setting on their own, but also on their (perhaps less technical) friends' and relatives' devices. Otherwise, if anything happens to your account or - less likely - the storage provider or their hardware, your data could very well be gone forever. I can't believe anyone would want that.
You don't need 'the cloud' to do that. Look into Syncthing. It does depend on an outside "discovery server" by default to enable syncing outside of your LAN, but you can run your own.
What's annoying is that synchronisation does't work for google slides or google docs. They are just synchronized as links to the webpage on my computer.
If you use Insync you have the option of converting to DOCX or ODT.
Insync has other issues though, my "sourcetreeconfig" is being downloaded as "sourcetreeconfig.xml".
