I was wondering why aptitude doesn't automatically purge not needed packages and keeps tons of configs I don't need on my disk. If I'd read documentation, I'd have fount out is sooner, but it has to came to me through random post to debian-devel about apt-findremovable.
The solution is simple:
echo 'Aptitude::Purge-Unused "true";' >> /etc/apt/apt.conf
