Training paces, especially in workouts, must have a high and low pace restriction. If the workout is written properly a goal pace, often an upper limit, is provided. However, I believe there must be a finite range. I think most amateur athletes would be happy to hit a goal pace and chip away at faster and faster times. On the day it can be a confidence booster and, maybe something to brag about. However, competent coaches use discretion and assess all of the variables before permitting this training habit. They know full well the extended recovery time following a really tough workout.
Too fast of a workout will cause the athlete to need prolonged recovery. Their legs could be dead for days, even weeks! Yes, they had a killer workout on Tuesday but their runs on Wednesday, Thursday and Friday have all been junk. Do they stand a chance in the weekend’s race? In the end what was really gained if so many days were unproductive?
I remember reading books by Dr. Jack Daniels, Joe Friel, etc. in high school and college. These coaches had calculations to figure out suggested paces for workouts. Every time, I thought “No way, that is too slow. I can go much faster than that. AND why is he/she suggesting so much rest!?” Then, like clockwork, I would run insane splits for the workout and feel flat for days after. Eventually, I tried the conservative paces and BOOM! I was feeling stronger day after day, week after week. The culmination of my quality weeks of training was making a difference opposed to attempts at blasting my legs on the track and recovering.
The same can be said about reduced recovery between intervals. Most of the time, a properly written workout is focused on attacking a specific metabolic system. Each metabolic system takes a known amount of time to recover. Chopping the recovery down makes it harder but does not facilitate the desired training adaptation and has increased risks of injury.
Harder is not smarter.