Maintain all versions of your files so that you can retrieve any of the old versions of the file easily without searching all over your hard drive.
Track which person changed what and when.
Control who changes the file to avoid more than one person changing the file at the same time.
At any point of time, any of the team members can get the latest version of all files from one single location, without the need to ask each member for the latest files.
Track progress - project manager or team leader can monitor the file change activity in source control systems to find out how much work each person has done on each day.
