This post is older than a year. Consider some information might not be accurate anymore.
For deb based distributions like Debian, Ubuntu, it is advisable to purge old packages (have status rc, r=removed, c=config).
List all removed packages that have config files:
dpkg -l | awk '/^rc/ { print $2 }'
Remove all old and unnecessary packages using apt-get:
apt-get purge $(dpkg -l | awk '/^rc/ { print $2 }')
apt-get autoremove
Can also be done with dpkg
