The site will only send graded results when you explicitly tell it to.
I often found that I would want to revisit some of my first essays because I realized that my grading rigor had evolved as I completed the stack. If the results were immediately auto-sent, I wouldn't be able to change my mind and re-evaluate those papers.
To send the graded results: log in, click on your assignment, then click on the "return graded work" tab. There you'll see the instructions for sending graded work out to all students whose essays are complete.