Well it'd result in a single file which if you have to copy on a microSD or USD stick might be easier. To also counter my own argument the result of dd can be mounted thus getting a rather useful directory quickly

But anyway my point was rather the opposite, that indeed in most cases rsync, rdiff-backup, even scp (whatever one is most familiar with) to a local NAS, remote server, etc is usually better, at least more understandable for somebody who isn't used to the process.