Why do you use timelines in history?

Time lines in history can help you have a small bit of an understanding about what you are about to read/it holds important dates during that empire/time period. I guess it can be a partial summary of important dates about that empire/time period, so it preps you for what you are about to read. But, if you were to actually read the summary on that chapter in your history book, then you will have a better understanding about that chapter compared to a timeline.