Actual Finish Date (AF)
The point in time that work actually ended on a schedule activity. (Note: In some application areas, the activity is considered "finished" when work is "substantially complete.")
Project Managers record the actual finish date of an activity so they can see whether it was finished on time. They enter the finish date into the project's schedule and scheduling software will calculate the impact on the other project tasks. For example, if a task is delivered late Microsoft Project will recalulate the estimated start and end dates of the successor tasks.
Actual Finish date is also important so that you know when resources are available. For example, if Sean the network engineer finishes his task early he may be able to move onto something else ahead of schedule.