Depends entirely on the design of the file system. In copy-on-write file systems, it's a necessity: you need to at least allocate a new metadata block that does

Depends entirely on the design of the file system. In copy-on-write file systems, it's a necessity: you need to at least allocate a new metadata block that doesn't record the existence of some file... and that's assuming you don't have snapshots keeping it allocated anyway. You can run into real trouble on btrfs if you fill it, it has no reserve space to protected from this scenario. ZFS at least reserves a fraction of the total space so that deletes are allowed to work even when the pool reaches 100% capacity.