What is the difference between using the Call and Branch methods in an activity step...

Call provides more robust debugging capability than Branch, while Branch provides better run-time performance.

Branch overrides the security restrictions of the called activity allowing you to easily test code; it will not run in production.

Branch creates a new thread to allow asynchronous processing, while Call runs in the thread from it was invoked.

Call returns to the originating activity, while Branch skips the remainder of the originating activity.