If you never heard of no washing rule the question from the title may seem confusing. Why in the world would you not wash dirty clothes? 
Washing the jeans used to be a no-brainer, you wear them and when they get dirty you wash them. But, recently I've been hearing more and more about not washing them. That way they'll keep their shape and last for much longer. 
The fact that your clothes last longer if you don't use washing machine is no secret, we use all sorts of tricks to keep all of our clothes in good shape: washing it in cold water or at least at lower temperature, using as much fabric softener as possible, hand washing delicate clothes, air drying anything that can shrink in the dryer. All of these tricks are well known and widely used. 
But leaving the washing  completely out? It seems very unhygienic and a bit radical. However, you can read this tip everywhere from blogs about maintaining vintage clothing to home economics magazines. 
Recently, even the CEO of Levi's (and who knows jeans better then them?) said you need to avoid washing the jeans. Apparently, you spot-clean when needed and freeze them if they start to smell weird. Low temperature will kill all bacteria and leave the jeans fresh and uhm... clean? Also, you can wash the jeans from time to time, preferably once a year. 
I'm not sure what to think about all of this. When I started to think about how often I was my jeans I came to shocking conclusion. All of my very good quality jeans I wash very rarely. It wasn't my plan not to wash them, and it's not like I avoid doing laundry (I actually quite enjoy doing it) just there was no need to wash them. They didn't lose their shape, they smelled clean and I'm not that clumsy and I rarely spill anything on them so there was actually no need to clean them. 
Skinny jeans and other pairs with elastane are a different story. I have to wash them after wearing them only two or three times, they stretch and lose their shape so fast and end up looking baggy and unfaltering. 
In order to make them skinny again I have to wash them and put them in the dryer, otherwise I will be walking around in jeans two sizes bigger.
At the end it's all question of common sense. If the jeans are dirty-wash them. If you need to shrink them in the dryer-do so after washing. 
All we can learn from this story is that we need to think more about washing our clothes too often. Avoiding unnecessary washing is better for the environment and more economical.