There's a thought that a serious athlete should always give 110% to every technical and weight room session and ALWAYS strive to improve in some fashion each workout, either thru height of jumps/plyos, speed of sprints, amount of weight lifted, or reps completed. It is true that when seeking improvements this is the mode you want to be on more often than not. However, it's difficult to train this way ALL the time.
The problem is when you put so much energy and put so much effort into every training session it places such a large demand on the nervous system that burnout is inevitable. The 2nd problem is temporary plateaus in speed-strength activities (such as a vertical jump or sprint) are an inevitable part of the process.
Even in athletes who make great gains over time, and those that do so using proper periodization, most trainees spend more time in states where their ultimate measurables are staying relatively the same than they do in phases where their ultimate measurables are improving. I see it all the time: An athlete trains hard for a month or 2 and puts several inches on his vertical jump. He continues to train hard and eventually hits a plateau, so he trains even harder and gets totally burnt out and begins to hate training.
It can and often does take time for gains to stabilize so that a higher level of performance can be reached. Continuing to bang your head against the wall during what is a natural progression of training is an exercise in futility. Training sessions and phases of training do not always have to be 100% intensive to be effective. It's still possible and advantageous to train and stimulate the muscles without going full bore.
The point is, regardless whether your goal is an improved vertical jump, faster sprint time, improved body composition, or increased strength, it can be advantageous to take it easy sometimes. I'm not necessarily referring to deload or unloading weeks, which are typically part of any given phase of training, I'm talking about planned periods of relatively less intensive activity where the goal is taking it a bit easy and not trying to set personal records. I often have vert and speed trainees take a month or 2 and perform submaximal jumps and sprints and use higher reps in the weight room with less intensiveness. Many of my trainees have actually made their best gains when incorporating 4-6 weeks of what I like to call these "country club" style workouts where they're basically just going thru the motions. Here is a sample 8 day schedule I like alternating upper/lower body workouts with days of low intense activity:
Sample Country Club Week:
Mon: Submaximal jumps/plyos x 30-50 ground contacts
Submaximal squats @70% of max: 3-4 sets of 6-8 reps (each set at least 2-3 reps shy of failure)
Romanian deadlift: 3-4 sets of 6-8 reps (each set at least 2-3 reps shy of failure)
Tues: 20 minute walk 20 minute full body dynamic mobility and static flexibility workout
Wed: ~15-20 sets of upper body bodybuilding style weight room work
Thurs: Repeat Tuesday
Fri: Repeat Monday
Sat: Repeat Tuesday
Sun: Repeat Wedneday
Tues: Start over
Phases like this are also a good time to experiment submaximally with new exercises and movements. The basic idea is get a workout in and stimulate the body but keep it relatively low key.
Phases such as these also offer several advantages:
1. They stimulate and condition connective tissue and stimulate muscular hypertrophy
2. They give your mind and nervous system a break rom the typical "go hard and go home" mentality.
3. They allow you to freshen up your joints and nervous system.
After a month or so of country club style workouts you'll typically be ready to go full bore and hit it hard again, and when you do so you will often immediately begin to set many PRs in the process.
For more information on incorporating a multitude of other aspects of proper periodization check out my Vertical Jump Bible 2.0