My take on re-using the /home directory is that not only data is stored
BUT if one re-installs programs after the upgrade or re-installation the
original format of the user's setup will return. For example if one
re-installs Thunderbird all the mail, addresses etc. are there without
problems. This is, of course if one uses the same user-name and distro
to setup the computer. I'm sure this applied top any configured program,
the configuration remains and is reused when re-installing. That's
another plus to keeping a separate /home directory.