as an example a simple date/time information we publish on our displays.
We found the font-sizes differ, please have a look:
This is what we want (and what looked similar in every window in V1.8.11/12):
This is what is looks in the preview-mode (Layout->Preview):
Inside the Editor (preview mode):
Inside the Editor (published / region clicked):
Inside the Editor (draft / region clicked):
As you can see, it is almost impossible to create suitable content.
Because almost every preview looks different.