Rotating cockroach baits for treatment is important because it reduces the likelihood of resistance developing. Resistance develops when an inherited trait that confers some tolerance to an active ingredient gets passed down generation through cockroach generation.
As the trait gets passed down, offspring inherit these resistance traits from their parents, and express even greater levels of resistance. By changing both the active ingredient and bait matrix you provide to the cockroach population, you reduce the likelihood of either resistance or aversion developing. A general rule of thumb is to rotate among products every three to six months.