When a package is upgraded, its old installation scripts and list of files are kept under /var/lib/pkgtools. After a while, a long running system can have a lot of stale files under these directories. As you can see with the following output:
punk@number5:/usr/libexec/slackpkg$ du -skx /var/lib/pkgtools/removed_scripts/
58244 /var/log/removed_scripts/
punk@number5:/usr/libexec/slackpkg$ du -skx /var/lib/pkgtools/removed_packages/
382968 /var/log/removed_packages/
Slackpkg is the tool that is usually used to upgrades Slackware systems, so it seems to be the best place to implement some routine to do a janitorial job of these directories.