I'm not sure about this squinting thing. We don't usually do that in class, because I just relish the brushwork as it is. What I love is how they can create images with just a splash of paint. That loose brushwork is not as easy as it looks and has more immediacy and spontaneity than using a very small brush and tight hand to get things exactly "right" as in a photograph.
I also just like the way the blobs of paint, if you will, create a new level of visual interest, especially if the white of the canvas or other colors shine through. I think this is from one of the waterlillies, but I just found it on a google search and love it at it is: a detail of his brushwork.
I'm not qualified to really comment on those guys, but I can bet that the artists themselves were squinting as they painted.
That's just it, I can't see the splashes of paint as anything more than splashes of paint unless I squint them into an image. I don't know if it's from nature or from training (I'm an engineer)
I guess the core of the matter is that I don't really care about technique or brushwork. I just want a picture that talks to me. And most of the impressionists don't talk to me. (The entire water lillies series doesn't grab me at all for instance)
One style that just crossed my mind is where they do the entire thing with many small dots of paint. Up close its just paint spatters on canvas but as you back away the image comes into view. Now that I can appreciate for the planning involved to get the image right. (Haven't an idea of what the style/technique is called)