Traditionally...
...flight training takes an integrated approach to teaching during which a student is introduced to foundational knowledge while simultaneously learning the mechanics of flying an airplane, but this method has its pitfalls...
Information Overload
Higher Cost
While integrated lessons allow a student to put into practice what he/she just learned, the amount of information is overwhelming.
The integrated approach really means time is spent on "classroom" type instruction but at flight instructor prices.
Why pay higher rates?
The Basics
Cramming
Mastering the basics first is a proven building-block method that makes the transition to flight training smoother, faster, and more enjoyable.
Putting off the knowledge exam means cramming to pass it during the late stages of flight training. Studying for the exam can be a distraction, destroy momentum, and even delay completion.
The best way to avoid these problems is to divide-and-conquer. Work towards the knowledge exam in ground school.