The libs feature of perlbrew is one I don't see used very often. At least, not by the developers I currently work with and have worked with in the past.
Sometimes I want to run a piece of code against the core libraries and only the core libraries. Sometimes I wrap a script up with Carton and want to verify that a base install + Carton can run my script. And sometimes I just want a place to install anything and everything from CPAN, play with new versions' features, etc...
This is where the libs feature comes in handy.
I have three sets of perl 5.20.3 libs:
$ perlbrew list perl-5.20.3 perl-5.20.3@carton * perl-5.20.3@dev
99% of my time is spent on the "dev" lib, where I install anything I want. The "perl-5.20.3" is just a base installation of 5.20.3. And the "carton" lib is just a base 5.20.3 installation with only Carton installed. And if I ever break the "carton" or "dev" libs, they're easily recreated from the base installation.
