When doing Kanban, you still need to do the equivalent of planning, assignment, estimation, retrospectives, delivery, etc. In Kanban, all of these activities are decoupled from each other whereas in Scrum they are all coupled to the iteration boundary.
How can this be applied to Scrum? Consider retrospectives. If you are just starting with Scrum, you probably have an iteration length of 1 month (or four weeks). From that it follows that you will have a retrospective once per month. If you eventually end up with an iteration length of 1 week, then it follows that you will have a retrospective every week. But this actually seems like the wrong way to set the cadence of retrospectives. Wouldn’t it be better to have the cadence of retrospectives meet the need for them? If it eventually makes sense to do a retrospective every week, doesn’t it make sense to get the benefit of them on a weekly basis when you are just starting Scrum?