Libreoffice will likely download the whole file.

But many others clients won't. In particular, any video player will _not_ download entire file before accessing it. And for images, many viewers start showing image before whole thing is downloaded. And to look at zip files, you don't need the whole thing - just index at the end. And for music, you stream data...

Requiring that file is "downloaded in full before program access them" is a pretty bad degradation in a lot of cases. I've used smb and nfs and sshfs and they all let you read any range of file, and start giving the data immediately, even before the full download.