It's also important, if we're refining composition to numbers and rules to define exactly which point we're talking about
Not surprisingly the elements of a good print ad, and photographic composition are very similar. Our eyes take in a more information than the brain can process. Because of that we focus on the most compelling information that the brain thinks is most important by a process called selective attention. Studies have shown that you can be distracted by visual information even when it’s not relevant. If it’s attractive enough, it’ll grab our attention even against our intention. Case in point your big arrows, they forced me to first see what you wanted me to see.
In designing a print ad you want to speed up visual processing, reduce cognitive load, and increase comprehension. Directing the eye allows you to guide the viewer’s eye along an intended path, to the most important information. Starting to sound familiar?
I was taught, both school and on the job, that when viewing a page the eye naturally follows an arc from the top/bottom left inside corner to the bottom/top right outside corner. Putting your most important points along that arc, made it easier to direct the eye from other areas of the ad, or in this case a composition. The first image is a good example of this in that the major elements, sun, cloud, person are closer to the natural path, and as a result even you big arrow doesnt detract the eye for long.
Using techniques like position, emphasis, and visual cues within the image will do more to guide the eye to the points you want the viewer to see than any grid.