In a few instances around wysiwyg you cannot set all options in the document default settings that are greyed out when the "Use document options" check box is checked. An example of this is: you can set dimension settings in document options, but precision is missing there. To set the precision for all your measurements to decimetre or centimetre instead of millimetre, you'd have to uncheck the "use default options" checkbox. This means that if you want to change the text height for all you measurements in the document, you cannot simply change them in the default settings, but you'd have to select all measurements (which can be quite tedious if you use them in different views). I know that this is not the only example where this happens, but I cannot find another example right now.