When using date or date-time custom columns there is an option for setting automatic time stamps based on certain events. You find this menu when editing a custom column. You can choose if the stamp should be set the first time the event is captured or every time.
Time stamps can be used in conjunction with Function columns to automatically track lead times for example. These lead times can be presented using Dashboards to visualize flows and processes, identify bottlenecks or track KPI's.