This is an extremely powerful way of programming because it more easily fits how we develop apps: requirements constantly change. Currently when behavior needs to be modified we are stuck with having to modify and understand old code which can be very tedious (in my opinion it's a crucial pain-point in software development).
Behavioral Programming makes it easier to modify a system without having to understand how it was built, but by observing a particular behavior. Once observed, the behavior can be modified, removed or completely changed incrementally, without having to go back and refactor old code.
Sorry if it's very abstract. I gave a talk about it in case it helps: https://www.youtube.com/watch?v=_BLQIE-_prc