Services attach to Composite or Task nodes and will execute at their defined frequency as long as their branch is being executed. These are often used to make checks and to update the Blackboard. These take the place of traditional Parallel nodes in other Behavior Tree systems.
The Default Focus creates a shortcut to accessing an Actor in your Blueprints and Code by setting the focus of the AI Controller. By setting the focus of the AI Controller to an Actor, you can directly access it from the AI Controller instead of accessing a Blackboard key.