What's the use of creating another CKeditor profile CKeditor comes standard with 2 profiles: one for filtered html, and one for full html. Now I added a third one, but whats the use? 

There are only 2 text format.. So why is it possible to create a third ckeditor profile?
Because it's also possible to create as many/few text formats as you want...

If you had installed Drupal using a non-standard profile, you might not even have full_html and filtered_html as text formats, and the CKeditor profiles would be different.

If you don't know why you need to add one...don't add one :)