This is true. I'll need to write a better description for them, and possibly show some usage in the tutorial.
By the way, Anuke, there's a thing going on where the next wave won't spawn until everything in the previous wave has been killed. In this way, you can box up one enemy and simply keep them there, and infinitely generate resources. I know this can result in people being swamped if their defenses aren't up to the task, but I still think it's better for the timer to continue ticking down even when the enemies are still alive.