WHY?
Dist-Zilla is a popular tool for building CPAN distributions. Build process is controlled by dist.ini, Dist-Zilla configuration file. A distribution author can specify license covering his work by a line in dist.ini file:
license = NAME
where NAME is a name of module from Software::License hierarchy.
Software-License is shipped with a set of popular licenses, from Apache_1_1 to Zlib, including GNU General Public licenses (GPL) GPL_1, GPL_2, GPL_3, including their "Lesser" and "Affero" variants (LGPL_2_1 and <AGPL_3>, to name a few).
So, if a developer wants to release his work under GPLv3 license terms, he should write in his dist.ini:
license = GPL_3
However, Free Software Foundation recommends using clause "license version N or (at your option) any later version". Unfortunately, Software-License distribution does not supply (out of the box) a way to express such clause.
Software-License-OrLaterPack fulfills the lack, at least partially.