An advantage is, you don't need any API or function calls. You can inspect or manipulate anything from the shell ad lib using cat, echo, and the usual commands. Plan 9 doesn't have ioctl() calls because it's not meaningful to send pointers across the network. Instead each device and service provides a file called cntrl (or something similar) to which you can read or write text - using cat, echo etc. So it's easy to write small test scripts or even whole applications, in the shell or any language you like.