What you are training
Delay and reverb both add space, and modern mixes use far more delay than beginners expect, because a synced delay adds depth without the wash that pushes a vocal backwards. The skill is hearing which one is on a track: a delay is discrete repeats, even when they are quiet and filtered; a reverb is a continuous decay. A slap delay of 80 to 120 milliseconds is easy to mistake for a small room, and a long diffused delay is easy to mistake for a hall, which is exactly why this drill exists. It plays a processed phrase and asks you to name the effect. Six rounds are enough to hear the difference between a repeat and a tail, and to notice how much of what you thought was reverb on your favourite records is actually delay.
After this drill, the plan: The daily plan drills delay-then-reverb routing next, the send structure that gives a vocal depth while keeping it in front.