On a basic level this allows results to be hidden from students until you're ready, but also allows for assessors to keep track of the state of individual student's assignment through a mark->review->release workflow.
In the grading page is where you can start to see marking workflow options appear, the default marking workflow state is Not marked, you can see this under the status column of the assignment grading page.
When grading an individual assessment there is now an option to set marking workflow state, any state other than "Released" will hide the current grade from the student.
It is also possible to change the marking workflow state for multiple or all students who have participated in an assignment.
Go to the assignment grading page and use the check boxes down the left hand side to select multiple or all participants in the list.
Now down the bottom you have an option to act on the selected participants
Click Go and you will be taken to a Set marking workflow state for (multiple) userspage, scroll to the bottom of the page and select the new marking workflow state and then click Save changes.
All the selected participants activities are now set to this new marking workflow state