It is. The main advantage that the negative has is that they only need to win 1 of what are called the 5 "stock issues" in order to win a policy debate round. Furthermore, the negative can also run something called a "counter-plan," which I talked about in another comment. That's basically something structured a bit like the affirmative plan, but which (typically) does not affirm the resolution. That's frequently enough to put the affirmative off balance, because the negative has essentially free reign to argue for anything outside of the resolution.
This seems like an advantage to the affirmative side. in that light, Ks are a strategy to negate the affirmative advantage.