Final answer:
A system log that tracks user activities provides accountability, ensuring that user actions can be traced and individuals held responsible for their activities within the system.
Step-by-step explanation:
A system log that tracks user activities on the system provides accountability. This means that the actions performed by users can be traced back to them, ensuring that users can be held responsible for their actions within the system. For example, if a user makes changes to a database, the system log would record who made the changes, what changes were made, and when the changes occurred. Therefore, in the context of a system log, accountability is the main purpose.