What is it for?
All of your employees have a default position that you choose at creation.
You will want to choose their most used position since this primary position will be chosen by default in the following Agendrix aspects:
Create a time entry (time and attendance)
Approve a time off
Time bank adjustments (time and attendance)
Where can I modify it?
You can adjust the employee default position under the Roles and positions tab of his profile. See the following screenshot!