Example of badly used vertical space
Niklas hated the scrollbars in the small text areas, while migrating a https://www.mediawiki.org/wiki/Manual:LocalSettings.php translation.
In my case, the problem is rather that so much vertical space is wasted and I have to scroll the page a lot in order to cut and paste text from one textarea to another. Some ideas for improvement that I throw for consideration:
a) adapt the height to the space required by the source text, keep it constant for the corresponding text area on the right side;
b) allow to move the division between right and left for all the textareas at once, not only one by one, so that I can gain more horizontal space if I want;
c) if it doesn't disrupt things too much (or when the changes above allow it), don't add scrollbars but always fit the height to what's actually needed to fit all the text.