Let's say Perk gets out of the inning, you go into the 9th tied with only Robertson and Roenicke left in the pen after already using Pressly, Duensing, Fien, Perkins and Burton being unavailable. If Casilla would have homered off of Fien in the 7th with 2 on would we be talking about why he didn't bring Perkins in then too? It was one inning earlier, same score, same amount of runners in scoring position.