You can do that because you aren't on a rolling release distro. If you are, you can still use system perl as long as all the cpan modules are in the distro catalog, which they usually aren't. That's when you need to switch to perlbrew. For extreme rolling distros like Arch, that isn't even good enough because the system libs change ABI frequently breaking XS modules, but at least perlbrew makes it easy to throw away and re-install a perl version.