Bruce Byfield discusses some lesser-known Debian package management tools in a Linux.com article: debfoster, deborphan and debsecan
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The answer is that these utilities allow for more conscientious system maintenance. Orphaned packages and system vulnerabilities are both potential security risks, so you can never know too much about them, even if your only concern is a home workstation. Debfoster, deborphan, and debsecan all give you information on your system that can help you make more intelligent decisions — and that makes all of them worth knowing.