The purpose of the shell is to allow users to interact with the grid. You can't do this in a conventional OS shell. Example: if you are using /bin/sh on linux-host-a and want to affect something running on linux-host-b, you can't. In a SSI shell, you can affect resources from a set of machines from a single shell.

You could offer something like shell scripting on that, but my system did not and there are better options. For example: have the resource manager expose a command that offers a DSL for making system-wide changes.