The "complete" feature was added to allow users a means to show that a record has not been altered. When a note is "completed," the note is rendered uneditable from within Insight Notes and the day/time of the completion is recorded in the user's activity log.
Some users, however, prefer to not "complete" notes because they have no need to do so. Notes that have not been competed can be edited at any time. They are auto saved when the user selects the "back" button and they are backed up just like competed notes. Uncompleted/Open notes can be exported and printed, as well.
Many users have a combination of open and completed notes in their notes databases.