I assume these are Zwift workouts.
This may be bollocks, but it's what I've figured along the way for myself.
There seems to me a muscular need to warmup (the flexibility and movement of muscles, joints, ligaments) and the metabolic/physiological warmup.
The muscular to me is the pure motion of just some low power solid cadence spinning. Lubricating the workings. The metabolic/physiological is getting the body primed for the work it's going to do.
For workouts, I try to tailor the metabolic warmup to the intensity of work I'm about to do. If it's going to be long time trial sets, I'll simply get myself to sweetspot for a couple minutes then back off and spin easy again before starting. You don't need immediate activation of that.
Now, for VO2 stuff. Yeah, I'll throw in some 10 to 15 second high power efforts then spin them out.
It's very personal. I've had to sometimes look at Zwift workouts I would want to do, then just create one myself or freeride then start the workout.