The main purpose of pictures and maps is to help enhance the story and to help the reader get a better feel of what's going on. The pictures should support the story, not the other way around. If a story is well written enough (a thing easier said than done of course!), an author needn't rely on the pictures so much. While it is true they do help to "break up" the text, I don't think there needs to be more than one or two per update. Unless they're really cool maps of course. I can never get enough of those, but that's just me.
I still go back and look at the map of the Germans invading the Washington DC area in Yogi's HOI tale.