I think that part of GrandFather's point is that you would be getting more of the application done in less time if you used appropriate modules wherever possible, instead of doing things from scratch.

A bunch of the code you need may already be written, and you may be able to find it on CPAN faster than you can write it yourself (and some CPAN author will have already put in a lot more time than you can possibly spend in solving a particular part of your task).

(update: Then again, depending on how well a given module is documented, or what it tries to accomplish in addition to the task that you need it for, learning to use it correctly might raise issues in some cases. The (inappropriately named?) XML::Simple module comes to mind... excellent module, really, but the manual is massive, and getting it to do something "just so" for a particular data set might take a while. Grain of salt, anyone?)