It's really up to you Michael. You have three tools in your signature that would have come with a Plug-It cord, so you could always use one of those.
I have one permanently attached to the Boom Arm, but I also have quite a few in individual Systainers that have never been used as the whole idea of Plug-It is the rapid connect/disconnect of individual tools; hence you're unlikely to need all three of your cables at once, so dedicating one to the Boom Arm shouldn't be an issue.