I recommend anyone to do a backup (I haven't always and it bit me). However, if you create separate /home partition you can keep that between re-installs, even re-installs of different distros. And you can also share the same home partition between multiple OSs you might have installed at the same time.
Sharing /home between distros can cause issues though: If one distro's $SOFTWARE is newer that the other distro's, they will still share the same dotfile configuration, and while most software is designed to deal with older configuration/database/etc files, older software many times cannot deal with newer files.
dist-upgrade is a lot faster and easier, and is usually well tested