Uhm what? If you use a "good" shell and don't do anti-patterns in it, the shell script will most likely be fast enough to not make any noticeable difference.

The upsite however is you don't need to take care of all that memory and allocation stuff and everybody can read it, change it and contribute to it.

That's my reason for doings most stuff in the shell. I even rewrite some small programs from Python with base/bonus utils (such as awk, diff and alike).