This was something that I had never considered in the past, but made sense to me from a physiological point of view. It is commonly accepted that you can only reach 90% of your VO2 max at threshold, however well trained your aerobic system is. As such, if you neglect your VO2 max development over the off season and your early base building phase, causing it to drop significantly, then proceed with threshold training starting in the middle of the base phase, the physiological limit of where your threshold can reach will be lower than it was when your VO2 max was fully trained. By boosting it slightly with, say, 4 weeks in which you do one targeted session at that intensity per week, your threshold has that little bit more room to move up into. When you then concurrently train both systems in the late build phase, you can both increase your VO2 max and squeeze up the % of it that your threshold lies at, resulting in a peak of fitness.
It then occurred to me that it might be a good idea to adhere to this sort of principle throughout your yearly training cycle, so that you repeat the routine for all other levels of training. If we define 7 rough levels of training as:
Easy, steady, tempo, threshold, VO2 max, anaerobic capacity, neuromuscular power.
then what I am essentially talking about is this: begin the season with 4 weeks of easy and steady training. In the next 4 weeks, rather than introducing low or mid tempo sessions, train at the lower end of threshold or the tempo/threshold border. Following this, then do 4 weeks where you do a lot more low and mid tempo work. I think it is likely that you will be much more comfortable at these sort of intensities having done some harder work leading into it.
We then repeat the process: do some VO2 max work before your focused 4 week threshold block, some anaerobic work before your VO2 max block, and some neuromuscular work before your anaerobic block.
One thing to consider is that for these later stages, it will become tougher to schedule me workouts as you will already be doing some fatigue inducing sessions at the lower levels, especially when you introduce anaerobic work (you will still be dong threshold and VO2 max sessions during this phase). However, careful planning will allow you to find a day each week to do this session.
I will stop short of giving examples of each type of session in this post, but the general idea is to do a decent but not maximal session at the intensity level that is one step above the system you wish to focus on. When you eventually then start work at your goal level, you will both find we session easier and be able to push harder.