Try actually using it. Conceive of an idea, and then attempt to achieve it.
The moment you start editing these little time chunks you'll start experiencing crashes, weirdness and bugs. I am certain of it.
The first time you place them, they're fine... but for a few weird glitches and peculiar aspects of their operation.
But editing them opens up a whole new can of worms on an entirely different level of disasterous.
Here's just a sample of the problems:
Add a move action. Set it as you desire. Now change the duration of the Action in the right panel. Notice the timeline has not updated to reflect the increase/decrease in duration. Wait for it... at some point in the next few things you do in the UI, it will update.
Duplicate this action. Right click over it, and duplicate it. Or copy and paste it. Notice the duplicate/copy retained NONE of the values in the original, other than the duration. It's not a duplicate, it's not a copy.
Set the duplicate/copy to mirror the first Action. You'll probably expereience some glitchy weirdness whilst doing this.
Now you have an oscillation, back and forth.
Deselect this node, do anything else you like in the Project.
Return to the node you created these actions in. And select the first of the actions. Change any value of the Move (Offset) X,Y,Z fields.
Select the "duplicate" to change its corresponding value to match your changes. CRASH!
Restart Xcode.
Return to your timeline, and attempt, again, to edit the "duplicate" action to match the first action. CRASH!
You now have a perfectly looping crash cycle and corrupted project. I have found no way around this problem other than deleting the object, and starting over.
And just about everything about this timeline and Action editor is like this. There is nothing that's stable about it. I don't think anyone actually uses it, as I've not found any complaints about it, anywhere.