The first case concerned your Hollow One plan, when dealing with Leyline decks the 2nd case applies.

Seems I need to spell out everything...

As for the Leyline case, the odds of your opponent having a Leyline and you having the answer is about .41 * .46 so it'll work in roughly 19% of your games vs. decks w/ 4 Leylines if you optimize your entire SB for just that.