My reasons some of which have already been mentioned.

1) CPAN will be aware of modules installed by YAST but not visa-versa. ie YAST will update the Perl module list but CPAN not the YAST install list.

2) More modules in CPAN, probably later versions (see what CPAN wants to update).

3) Maybe even get a better module to do the same task.

4) More control if you build it yourself. Get the options you want.

5)What if YAST update decided to update a module that then broke your proggy?

6)It's more fun to get and build with CPAN/CPANPLUS, especially when it doesn't always work and you have to delve to sort it out. You can learn a lot that way.