Why not? Why not go into a game knowing you're going to try and get a majority of the innings pitched from two guys that are built up as starters and capable of each giving you at least 5IP, when your 40 man pitcher roster is chock full of those options compared to having a deep supply of shutdown relievers that can be relied on for ~3-4 appearances per week? I'd much rather take a piggy backing approach with 1 rotation spot than roll with a 6 man rotation or shuffling a guy who should be starting somewhere into an inconsistent bullpen role at this point. So let's say the plan is to piggyback Chacin/Peralta 4 innings each. 1) Chacin is horrible and can only go 2. Down 6-0. Now you want to use Peralta in a blow out game? 2) Chacin is pitching great. Up 6-0 after 4 innings. You want to yank him just because his 4 innings are up? 3) Close game, Peralta replaces Chacin after 4. Now in the 6th inning Peralta is AB with bases loaded. You're going to let him hit just because he needs his 4 innings as piggyback starter? I know the replies will e, well it doesn't have to be THAT rigid. If it's not, it's not piggybacking. Bringing in Peralta for to innings of relief is called a relief pitcher, not a piggyback. Very, very few games where it would make any sense at all to have one guy pitch roughly 4, then another guy pitch roughly 4. 1st off I'd never pick Chacin as one of the starters currently in the rotation to piggy back - but I'll just keep referring to him when responding to the rest of your questions. 1 - yes, absolutely. It's a blowout game that the team has limited chances to win. get Peralta his innings and see where things go with the game come inning 7 or 8. This way the bullpen is preserved in case one of the starters not being piggybacked has a blowup game. 2 - no not at all - if a starter is pitching great and is capable of giving you ~100 pitches through 5+ innings, you let him make his full start. I'd prefer for the starter in a piggy back situation to go at least the first 5, so I don't know where your 4 inning suggestion comes from. 3 - again, not sure why Peralta is coming in after 4 if Chacin is pitching ok - particularly when considering who's due in the lineup to start innings 5 and 6. Ideally, Peralta would enter the game in the 5th/6th/7th inning and come in right after Chacin is pinch hit for in his last AB. If Chacin is having difficulties getting out of his last inning, you'd use the best available bullpen option to try and work out of a jam, so Peralta comes in at the start of the next inning. if there's a late game situation where the pitcher's spot is due up and a PH is an obvious choice, then sure - you pull Peralta and let him get the rest of his pitches completed on the side in a simulated game to keep him stretched out. Should the NL finally adopt a DH, then this concern is completely mute. None of the scenarios you presented really are good arguments to avoid this strategy.