D5. Single and dual factor training
Specializing and advanced programming techniques doesn't inherently mean: use a body part split routine.
The body part split routine is largely a single factor programming model. The idea is that you train, say, Monday. Fatigue yourself a bunch. And then recover fully before entering another training session next Monday.
This works for bodybuilders because they can do a lot of different exercises for different body parts to ensure even development. And a consequence of this is a shit ton of stress, so, hey, why not rest an entire week? It fits the lifestyle and it's fine.
But what if, say, you play ultimate frisbee on Wednesdays? Suddenly thrashing your legs on Monday doesn't sound like that great of an idea.
There's also a dual factor programming model, which acknowledges and allows for fatigued training. Meaning you don't dig yourself into as huge as a hole and you use fatigued accumulated over time.