The first image above is from Frank Santoro. One of my favorite artists, Frank offers a correspondence course on making comics (and also did a cool contest for aspiring, or non-aspiring, artists to enter their own comics in), and it all revolves around the grid. Basically - and I may get this wrong - Frank feels that working within the guidelines of the grid gives comic artists a solid base from which to craft their stories. Allowing the storytelling to reveal itself within the strict panel layout can free people up and also make it easier for readers to read their comics.
Coincidentally, in dong a re-read of Stray Bullets (the next two images, written & drawn by David Lapham) to prepare for its imminent return, I found that Lapham was utilizing this same grid in his seminal series, almost two decades past. And, yes, the storytelling in Stray Bullets is wonderful, and keeping to a strict grid allows the audience to focus on the story and not on any stylistic flourishes that might come about from a more "free-form" approach to the page. It's interesting.
Another artist whose work I admire greatly is Scott Morse. He, too, utilizes a set panel layout in much of his work - but his "grid" consists of three stacked panels that spread across the entire page. Like Lapham, Morse will break up his layout when necessary, but much of the work he has both written and drawn (in the Strange Science Fantasy pages above, as well as Visitations, off the top of my head), utilizes this layout. And, again, the expressive storytelling that is accomplished within the strict panel grid is amazing. Good stuff all the way around.