The Default Value Macro allows the author of a template to have a default value assigned automatically to a placeholder. When doing so, the field for the respective placeholder in the Placeholder Replacement Dialog is prefilled with the value in the macro, but can, if you want to, still be modified.
The Default Value Macro has to be put where the Page Tree Creator is invoked to copy a page in order for it to have any effect. For example on the page with the PTC Button
With version 8.x the Default Value Macro can also be put on an ancestor pages
Enter an existing placeholder (e.g. __project_number__)
If checked, then the macro body content won’t be shown on the page in view mode
If checked, the placeholder will still be editable in the replacement dialog. So it will be just a proposition
The default value will be placed inside the Macro Body. The value can be rich format
Please visit Reuse Placeholder Values (PRO)