Imagine how to animate doors, effects, cameras in synchronized with character?
Scene Timeline is the best solution for you! no more need to remember frame numbers something happen.

Timeline Editor was introduced in Unity 2017.1 instead of this tool.
Unfortunately, it can be used only when your project requirement allows you to use Unity 2017.1 or later, and also you need to update existing scene structure ready for use of Timeline Editor.

Scene Timeline works without any changes to existing scene structure, and more friendly interface like Maya, MotionBuilder and other DCC Tools.
And also this tool can be used on older versions of unity prior to 2017.1.

If you are not able to use Unity's built-in Timeline Editor due to production requirement and/or scene structure.
Scene Timeline is the best alternative to Unity's.