True, but I have yet to find a reason to prefer full (or even incremental) backups over CoW. Full backups are just too big and slow, and good reliable open-source and cross-platform incremental backup software is hard to find.
I've found using Syncthing for Client-->NAS-->Off-site with BtrFS snapshots on both servers to be just perfect (of course, YMMV).
> good reliable open-source and cross-platform incremental backup software is hard to find
I've been using rsnapshot for at least a decade, and it's available wherever perl and hard links are available (which isn't windows, at least pre-WSL).
>Copy-on-write (CoW or COW), sometimes referred to as implicit sharing[1] or shadowing,[2] is a resource-management technique used in computer programming to efficiently implement a "duplicate" or "copy" operation on modifiable resources.[3] If a resource is duplicated but not modified, it is not necessary to create a new resource; the resource can be shared between the copy and the original. Modifications must still create a copy, hence the technique: the copy operation is deferred to the first write. By sharing resources in this way, it is possible to significantly reduce the resource consumption of unmodified copies, while adding a small overhead to resource-modifying operations.