Vlad, I know for me, the 39 focus points can be a bit much and confuse the camera when I am trying to focus on a specific item in the viewfinder. As an example, if I am taking a pic in a room, and I want to focus on a picture on the far wall, using the 39 focus points spread out across the viewfinder, the camera may focus on a lamp, or some other object instead of what I want to focus on. As a result, my target picture may or may not be in focus depending upon what F stop I am shooting at. Does that make sense? In other words, I think the 21 pts of focus narrow down the "target area" that the camera focuses on, and that is beneficial for most folks. Personally, I rarely ever use the 30 pts unless I am shooting landscape shots.