One of the essential and fundamental elements why Scrum is becoming very important is that when the team sits together to discuss and groom the stories, is because of the grooming and tasking of efforts.
When the product owner or manager brings the intent and create a high level user stories, the team does detailed study of the story in understanding the value that feature or functionality brings to the user and starts writing the tasks to be done to meet or build the end user functionality.
A Scrum Master has to enable the team to write the story and detailed tasks required. This is important because each day when the team comes to work they should not squander around OR search OR go back to drawing board as to what needs to be done. Ideally the team member open the agile tool > go to the user story > read the tasks > start working on each task by task. This way its a total heads down approach to crank thru the work required of the sprint and provide the required user functionality by the end of the sprint.
To conclude, it is extremely important that the entire team understands this way of story grooming is must and should, otherwise the daily stand up calls or any other adhoc meetings happen during the sprint will not yield any value and simply Agile wont work.