Can you imagine an image that you would include in a large show, when you have people's attention but which you'd hesitate to present as a stand-alone image?
I can. It's similar to the difference between what's known in the world of photojournalism as "wild art," which is a stand-alone picture that doesn't even illustrate a story...often the result of "cruising for features"...as opposed to the sort of images that flesh out a picture story where the images are equal to or even primary, relative to the text. On a page like that you might have between three and six photographs, some of which work in a way that's essential while not being images that would be published separate from the group.
Sometimes subtle images aren't just ok, they're critical.