The AddTickPrerequisiteActor and AddTickPrerequisiteComponent functions, which exist on both actors and components, will set the actor or component on which the function is called to wait to tick until the specified other actor or component has finished ticking. This can be particularly useful for things that happen at roughly the same time in a frame, but where one actor or component sets up data that the other will need. The reason to use this over a tick group is that many actors can be updated in parallel if they're in the same group. Making one group of actors move to an entirely new group might not be needed if those actors are only individually dependent on one or two other actors, rather than needing to wait for the whole group to finish before before ticking.