This generally isn't a thing simply because it's not practical. Boom Tubes and Zeta Beams simply invalidate the strategy of using forcefields as a wall to cut yourself off from the world...
True. Though there is at least one Elseworlds setting in which we see a force field surrounding Earth that is proven to block zeta beams in the most brutally direct manner possible- someone finds Adam Strange's dessicated corpse in Earth orbit, where the force field intercepted his transportation. Poor bastard.
and it also does nothing to effectively defend against being conquered by a foreign power if you do not have some other defensive measure (which would rely on having capabilities/resources beyond just one planet) in order to really be effective. Even people like the Daxamites, who have had members so isolationist they refuse to breathe the same unfiltered air as other species, are forced to bend to practicality and interact with others in order to effectively defend themselves from interstellar threats.
True, but this is a bit like saying that a city gains nothing from being defended by walls and forts if it doesn't have an army to garrison it.
For example, as I recall, the Daxamites have the powers of Superman but a disastrously serious lead allergy/vulnerability. They would gain some major advantages from being able to keep up some kind of planetary barrier shield that prevents an enemy with FTL spacecraft from just warping in, dumping millions of tons of lead birdshot all over the place, and warping back out. A planet with more conventional inhabitants still, in principle, needs to worry about problems along the general lines of "a drive-by shooting, with nukes."
Having a planetary shield, even if you only raise it when intruders threaten your planet, or perhaps
especially in that case, has its appeal.
Biot is probably a better hypothetical example. Takron-Galtos requires too much movement of materials (the whole planet is a prison so it needs to get all of its resources like food, fuel, uniforms and more sourced from other planets which means even beyond prisoner intake and exiting Takron-Galtos can't keep the planet cut off for very long and remain effective at doing it's job. Biot on the other hand is a world that's very much intended to be cut off from everything and nobody would move stuff onto or off of the planet anymore.
Given that Takron-Galtos is an entire planet, you probably
could use automation or prison labor to produce most basic consumables like food and fuel. Supply deliveries for things like uniforms and weapons that you really don't want sourced on-planet would be less frequent, then.
But you're not
wrong, and of course there are always downsides to that sort of thing, and I'm not saying that you're wrong to say what you do about Takron-Galtos.