By default if rsync sees any difference in metadata (timestamps), it just copies over the file fresh - first to a temporary file and then renames over the origi

By default if rsync sees any difference in metadata (timestamps), it just copies over the file fresh - first to a temporary file and then renames over the original. To do an in-place update you'd need to specify an arg for that. And even then, it needs to do a full read of both files to compare, so all it saves on is bandwidth.