If you have a chunk in the diff-view which is longer than a few lines (imagine even a dozen lines), the horizontal scrollbar is not accessible, which means you can only navigate long lines in a very small area of the diff. Now you have to scroll way down to the end of the chunk, use the horizontal scrollbar (how much you need to move it?) and scroll up again to actually see the area you want.
I think nobody want to work with this bahvior and this should be improved to permanently show (all relevant ?) scrollbars ...