How do Altium Designer 20.2.4 Schematic Defaults work?

Question

I'm trying to use the Schematic -> Defaults to predefine how I want every part of my schematic, but I found it a bit confusing.

First of all, I can't make the changes that I want. Now I'm trying to configure all the font sizes to 8 or 6 (the predefined size is 10), but when I place a new component from one of my libraries, the font has the original size. For example, it happens with the component designators or parameters:

The first and second images are the defaults in mm and mils. The other thing that I don't understand is why I have to configure everything in both units.

I think that it could be a bug, but I really don't know.

Answer 1

Font sizes for placed components comes from the schematic symbol in the library. You could modify the symbol library to have the desired changes be permanent. The schematic defaults in settings apply to basic elements added to a schematic in the editor, ignoring components brought in from the library, unless you check Override Library Primitive.

Override Library Primitive (Preferences dialog only) - enable this checkbox to override the primitive settings defined for the designator object in a library. Therefore, when a component is placed, it will adopt the primitive settings you have defined in the Preferences dialog, rather than those that have been defined for the component in the library.

(This option is shown in the screenshot you included in your question, at bottom right.)

There are pros and cons with either method, so it will depend on your workflow and/or company policies whether you should modify library items or override using this option in preferences.

For more information, see the official documentation in Schematic Placement & Editing Techniques in Altium Designer.