In BTLimiter, what is the purpose of the blackboard?

[dfego]

I'm writing my own decorators and in looking at BTLimiter, I notice it uses the blackboard with a unique key for that particular instance. How does this work better than simply having a variable in the node to represent this value?

[ThePat02]

I think this was mostly done to demonstrate how to do something like a unique key. I don't see any other use or why past-me did this.