Work stuff is running over, so I'll try to summarize quickly. You draft or manage enough IP to essentially get you through 120 games and you draft or use $200k scrubs to get you through the other 40. Essentially, it's choosing your battles. You put your A squad against division rivals, and against teams you might compete for WC against, and your scrubs or lesser squad against interleague matches. Similarly, if you're in a league that you end up short IP, You can selectively run a weaker or fatigued crew out against targeted opponents to maximize your wins against teams you need to beat. Throw a scrub every 5th or 6th game, for example to keep your other guys fresh. You'll likely lose that game, but since you didn't have to pay for those IP, the rest of your team should be higher quality to win the other games at a higher rate. You can maximize this by design by also drafting scrub hitters to play in those scrub pitcher game and taking higher quality part-time bats for the games you want to win.
The changes to injury rates, the PA/IP minimums, and AAA salary caps for guys being sent down all make this much harder to run effectively in an OL these days, but themes that don't have minimums or injuries on, this is still quite effective.