Hi @mh12,
If you unsync a file, the local content is removed and the file is replaced with a placeholder file. A placeholder file is a representation of the file you have in the cloud. It doesn’t have any data in it (0 bytes) but allows you to see what you have available in your linked storage.
For backup, many folks will use odrive as a form of backup (or protection), although it is not a traditional backup solution.
There is a post I wrote a while ago that goes into sync vs backup and how I use odrive for my own needs. It may be of interest to you: