"A robust package manager backed by a large open source software
repository is useful for more than just convenience. It allows the
user to test software they may have not previously heard of. Being
able to quickly install a piece of software you've heard about to
give it a test is extremely useful.
"We also need to have the ability to test things that may end up
on production systems. Ruby or Perl modules, for example, are often
needed when developing automation scripts. Of course, this often
leads to frustration if we aren't careful. Say a fancy new Perl
module is available via CPAN, so we install it and start to depend
on it. Then when it come time to run the new script on production
server, which probably don't use CPAN, we find out that the module
isn't available as a package."