Progression levels do two things…they keep users more engaged throughout workout progressions and they give users a way to place a given workout’s difficulty with respect to that user’s own ability AND the relative difficulty of other workouts.
A lot of times I would find myself really engaged during threshold workouts but kind of going through the motions during VO2max workouts. Progression levels keep me more engaged during all workouts, all week long. It gives me a framework to keep ‘achievable’ but consistent progress in all types of workouts. Not just the type of workout I’m preoccupied with.
Also, if I want to dial things up a little bit and use that “Alternates” drop down, progression levels serve as a guide so I can pick a workout that is definitely more challenging but not over-the-top-make-my-eyes-bleed hard. This is actually the number one thing for me. I get a systematic sorting of a given workout type with respect to the workout I want to replace and with respect to my own current state of fitness.