First and foremost, do you know that not all teeth require crowning after root canal treatment? It depends on which tooth and the amount of remaining tooth structure left after root canal treatment is completed.
If you just had the nerve of your molar or premolar treated, you will need to crown them as these are the back teeth used essentially for chewing and are subject to heavy masticatory forces and stress.
On the other hand, you may not need a crown if your front tooth has been root canal treated and there are no major tooth structure loss, except for the “hole” created at the back of the tooth during root canal treatment.
Hence, crowning serve to protect a tooth from fracture as it is rather weak after root canal treated. Without crown treatment, you are subjecting the tooth to potential crack and hence extraction if the crack is extensive. I am sure you do not want to waste the time and money invested in root canal treatment, right?