"For all the efficiency and continued evolution of Debian's APT
tools, some gaps in package management functionality remain. One of
the largest ones is that, when a package is removed, any other
packages that depend on it are not removed. The result is a growing
number of orphans on the system--that is, packages that serve no
purpose for the system as a whole, although in some cases they
continue to be useful individually. Similarly, while you can keep
track of security announcements for Debian or distributions derived
from it, the basic package system has no way of telling you which
vulnerabilities might affect your system. To compensate for these
lacks, you can turn to a group of housekeeping tools that make
maintaining your Debian system easier and more efficient.
"As experienced users might expect, you need to have some sense
of the Debian package and repository systems to make full--and safe
user of these packages..."