I've been noticing a technique that the designers of Android: Netrunner seem to use quite often: namely, that of creating fallback cards that act as a silver bullet to certain strategies. Feedback Filter is a good example of this: if decks revolving around a killshot with net damage made possible by brain damage lowering the runner's hand become popular, feedback filter would be a perfect counter to them. This doesn't mean those archetypes can't become good; just that they can't get too good.
Plascrete Carapace is an example of a balance sink card that ends up being used. For a while, while Tag and Bag was one of the absolute best archetypes, Plascrete Carapace was needed three times in every runner deck. It is still common to have even in a non-tag me deck, but is nowhere near as necessary as before. And yet the relative power of T&B is still around the same; it's lost prominence due to the rise of NBN FA, but the fact that Plascrete Carapace does not always go up first turn against Weyland makes it better again.
Balance sink cards like Plascrete Carapace act like a chemical buffer: inside a certain range, the power of an archetype increases by much less than it would if its silver bullet did not exist. One possible reason for the designers to include this sort of card is to make the meta much more stable: if NBN fast advance became the only viable corp deck, The Source would make it still within range of the other corps. This sort of cards also acts as a way of forcefully introducing variety into the metagame, because the chosen archetype of a meta without variance quickly stabilizes back as soon as the runner decks begin to include the silver bullets.
What this looks like from the standpoint of a player is that many times, a card introduced in a datapack seems useless, and
is in fact useless. Like reaction cards in dominion that hurt the attacker
1, they will probably never be used, but, and this is on purpose in Netrunner, will decrease the effectiveness of their chosen target or at least give it a boundary over which it cannot pass but slowly. So don't be disappointed when you crack open the new data-pack and find a Restoring Face: it's doing its job in the backround, unseen yet efficient.
1 See
http://forum.dominionstrategy.com/index.php?topic=699.0 for why there aren't reactions that hurt the attacker in Dominion.