To answer the "when is shell preferable" question:

perl usually resides on /usr, which makes it hard to use for things like boot scripts (one of which will probably be used to actually mount /usr).

Also, it has a size (after doing a quick rpm -i perl) of 30+ MB. In contrast, the network boot image I use at work to recover machines has a total unzipped size of about 16MB, which includes a regular glibc, bash and all the utilities you'd ever need (well, close).

I'd say those are the two main reasons for me to use shell scripts: unavailability of Perl, and the size of a standard Perl installation.