So far it seems best for placing on a planet for highly valuable stuff, like a factory with zenith power generators on it.
A counter guard post and a specific AI type can send in waves at any of your planets no matter if its directly connected to a hostile planet with a warp gate or not.
So technically even your home planet is in danger by this.
By using the warp jammer on planets deep in your territory you are removing that planet from the warp wave list.
Ya, you could leave the planet un-colonized but I guess its for people who want to truly conquer the galaxy.