Strength Training is Technical

I became interested in lifting weights when I was 17.  I thought of myself as skinny and I wasn't happy with how I looked.  I decided I wanted to learn to lift and gain muscle mass. My first book was Arnold's Encyclopedia for Modern Bodybuilding.  After that I read the muscle magazines as much as I could and read training articles online in my spare time.  This was the beginning of my journey training in the gym. 

The biggest lesson I learned from reading those magazines and books was that FORM was absolutely one of the most important factors when training.  If I wanted to build muscle and look like the guys in the magazines I understood I needed to learn how to do the exercises properly.  

In strength training there is a concept that influences MUSCLE RECRUITMENT.  Muscle Recruitment  refers to the muscles you use to do an exercise.  A side note, just because an exercise is intended to train certain muscles does not mean that is happening with you!

Weight lifting exercises are each designed to target different muscles.  If you have proper form you will RECRUIT those muscles.  If you have poor form or postural challenges you may unintentionally recruit muscles that you did not want to train.  If you prioritize load over technique you certainly will fall into this pattern.   You will develop new movement habits that increase your chances of getting hurt AND your body will look a bit out of place.

This is one of my most valued rules - do not compromise technique for load. 
Unless you are training competitive strength athlete (e.g. weightlifters, powerlifters),
loading is not the primary goal.  Functional Strength is.  Therefore the function/recruitment patterns are more important than the load.  Displacement of load is not highly correlated with function and transfer to specific sporting movements.

- Ian King, "How to Teach Strength Training Exercises", p.28
-Ian King, "Legacy, Ian King's Training Innovations", p.46

When you design your strength training program.  Determine load based on what you can complete with impeccable technique.  Once you allow deviation on form you are "leaking oil" so to speak and the car is gonna crash.  And it ain't gonna be pretty.