Some classes should be used on screen components, however, for new developers it is difficult to know what they should be because the are listed on "ExcludeFromPickers" so that they can't be selected.
Here is a list of common ones that should be removed from this section:
ActionAdd, ActionChange, ActionDelete, Badge
Application_Menu, Menu_TopMenus (needed when building a menu)
Form, EditRecord, EditRecord_Buttons
EditableTable
Filters_Wrapper
TableRecords, TableRecord_Header, TableRecords_TopNavigation, TableRecords_OddLine etc. (used when creating a table component, needed on the table widget styles)
We shouldn't need the classes that are built into Outsystems web blocks, but when users are using the components on the screens, you shouldn't have to remember what the classes are called in order to style the components correctly.