The Timeline allows you to view to all the events that have taken place since an engine's creation in reverse chronological order (most recent events are shown first). To access a specific engine's timeline, simply click on the icon on the right side of your dashboard.
Using the Timeline enables you to spot which changes might have affected your engines' performance negatively or positively. You can filter for specific types of changes to your engine (eg. uploaded data, build jobs, etc).
You can also choose to archive specific builds in order to be able to restore them in case you need to. Simply select the archived build you wish to restore from the drop-down menu, and click on the blue 'Restore' button on the right hand side.