October 7, 2014
When running an aptitude purge <package>, unlike with remove, the package’s configuration files will also be purged.
However, while in both cases the unneeded dependencies are removed, they’re not recursively purged when using purge. This results in all <package> dependencies configuration files remaining on the system (and there can be a lot if you install recommendations and suggestions, which is the default).
While I don’t know a way to make purge recursively purge the dependencies configuration files, you can run aptitude purge '~c' to remove the configuration files of all previously removed (but not purged) packages.
See also aptitude search patterns for all the neat stuff you can use in aptitude queries!