In the UK - and perhaps also in other countries - it is often used to interleave text fields into the control descriptions, for example "Take care when crossing road", or "Courses close at 17.00" or "Safety bearing North".
The "Additional text" is a field associated with each control, which allowas you to add a text for the control. This text will then be shown in the control description, underneath the control. This means that the text will appear on all courses that visit the control, and the text will be identical for all courses.
This does not mean that you cannot have a course specific text ("Course 1", "Course 2" etc) on the map. This text will appear in the control description header, or, if you configure that you don't want control descriptions on the map, as a separate text.
The menu "Course Overprints" / "Settings" / "Control descriptions" allows you to configure if you want control descriptions on the map or just the text that identifies the course.
In version 8, which I am working on, you will have more options to configure texts, and format these texts individually.
-Finn