Judging by others pictures can be misleading. Did the grower defoil prior to leaves turning yellow, or after?
The answer will tell you more about the technique used.
Personally, on the long branches that are too close together, defoiling a bit can open up the area and expose more bud sites to light and air. You want that.
Removing too many leaves will hurt yields and be counterproductive.
Now the other option is to leave the leaves be. In that case, older leaves that receive less light will eventually yellow and die off. These leaves should be removed from the plant.
Eventually, while the removal of nutrients (specifically nitrogen) happens... all leaves begin to yellow. Some growers remove all yellow leaves at this point in time (even if they didn’t defoil at all previously).
Hope that makes sense.