Absolutely without a doubt the biggest step up I ever made was to learn how to write CPAN modules myself, not just use other peoples.

You learn so much from it. Writing clear and effective docs, testing properly, component-based development, dependency issues, cross platform development.

It's like the difference between being able to build things with lego, and being able to create your own lego pieces.

Once you get used to it, you'll find that you start building work projects as CPAN-style distributions as well, and this can bring huge wins in terms of maintenance and reusability.

And this drives an understanding of not just programming in Perl, but in creating large applications and large systems in Perl. And the lessons from that drive understanding in creating large applications and large systems in general.