Well, as usual, “it depends.” Perl is a very modular system ... unlike, say, PHP, it consists of a tiny language core which “uses” everything that it requires in order to do any particular thing. One way to do this, say in a production environment, is to standardize all the systems to a known-good configuration. Another way to do it is to bundle with the Perl app everything that this Perl app needs to run, and to place those components into an isolated directory that only this app will reference. On the one hand, it is “wasteful.” (But, who cares anymore?) It is isolated, therefore very independent.
As a self-confessed “sysadmin,” you are more likely to want to set up and maintain the first scenario, rather than the second. You will standardize the configuration of every production system, every test and build system, to the same base set of packages, instead of choosing to follow the perlbrew advice. Neither approach is categorically right nor wrong.