Not going "by the book" can have it's advantages in training

Performing certain exercises "by the book" may sometimes be impractical given the nature of the exercise and the body strength needed. For example, a good way to perform pull ups is to utilize a band which can off set body weight and make the pulling load of your body feel lighter when you don't have the body strength to perform pull ups without the band.

In  your training don't be hesitant to make training adjustments based on strength, flexibility, etc.  There are a bunch of ways to vary exercises and drills based on a number of different variables.

"By the book" is not always practical, and sometimes can lead to finding different ways to accomplishing the same task (exercise/drill!)