When you submit the offer, the system closes the Create/Edit Offer form and the Add/View Notes dialog box automatically appears where you can add a note to the candidate profile if you want. This is optional, and you can click the X at the top right of the control to close the control without adding a note.
The application adds the note both to the Add/View Notes dialog box and to the Applied Jobs section of the candidate profile, next to the offer status.
If there was already a note next to the offer status (for example, from a previous offer), the new note replaces it. However, all past notes are stored in the Add/View Notes dialog box. See Candidate Notes.