What you are training
Parallel compression is the technique behind most modern drum and vocal sounds: a heavily compressed copy blended under the dry signal, so you get density and sustain without losing the transient. Done right it is the difference between drums that sound recorded and drums that sound produced. Done wrong, the blend is too hot and the kit turns into a wall of hiss and cymbal wash. This drill plays the dry signal, the crushed signal, and a blend at a hidden ratio, and asks you to judge the amount. Learning what 20 percent sounds like against 40 percent is the whole skill; the plugin settings are secondary. Six rounds on drums and vocals teach where the blend stops adding weight and starts adding mush, which is exactly the point most home mixes sail past.
After this drill, the plan: The daily plan drills blend ratio on drums first, then vocals, then teaches when to leave it off entirely.