What is the point of cutting the same manga panel in two? This is hard to put in words so let me illustrate (these are excerpts from two separate mangas):


What do these cuts accomplish? Usually in comics each panel shows a different scene.
The primary reason for doing this was to draw the reader's eye up towards the sky, towards the billboard. A side-effect is that it also looks more visually interesting than a single unbroken scene would have. The blank space between the panels gives your brain something to do, as it mentally fills in the gap.

So, we can assume this is done in order to make the manga more visually appealing and interesting to look at. Other times, this could be a random or artistic choice.
(source)