I am a developer on the Catalyst team working on the timeline and I need some specific feedback:
Do you find the list of objects on the RIGHT hand side of the timeline useful? What would you think if the list on the right hand side was removed?
A transition is an animation between two states, so the timeline visualizes a transition by putting information about each state on each end of the timeline. On the left hand side is a list of objects in the starting state and on the right hand side is a list of objects in the ending state. The list of objects on each side is the same, but an object appears grayed out if it is not visible on one of the states.
The select behavior is different between the list and the right and left hand side:
Click object on RIGHT side > selects object, view START state
Click object on LEFT side > selects object, view END state