Thoughts about closed applications

When you have an important application that is used by many people you do not control, maintenance and support quickly becomes a nightmare if everyone is able to make modifications to the application.

Note that modifications can also be made by accident. And what happens if an unrelated system administrator installs an unrelated package that updates one of the CPAN modules to a version that doesn't work with your application?

Best of both worlds: closed package + full source.