There's a ton of data in other sports (distance running for example) that shows quick increases in workload cause injuries. So if you're going to train for a marathon, going from zero miles a week to 40 miles a week in 18 weeks is likely to cause an injury because your muscles, tendons, ligaments and joints aren't accustomed to the load being put on them. Some of that can be minimized by running slower paces, but it doesn't eliminate the risk. I think you get into a more nebulous place when you're talking about pitchers because these aren't guys off the street who've never done this before, but in a case like this, you're asking someone to go run a marathon at their 10K pace (in terms of velocity thrown and spin put on the ball) so it stands to reason that backing off that breakneck pace like the White Sox did with Crochette last year makes a ton of sense.