when I change one of my rules, there is the button "Update Rule". I am not sure... why do I need to click on that button? Is it necessary or is pressing "Done" enough? I always push this button, but not sure if necssary.
As mentioned above, "Done" and "Update Rule" do the same, except "Update Rule" keeps you in the rule instead of returning you to the previous page. Either is necessary if you change trigger events or (I think) required expressions, but just changing actions doesn't need either--though in most cases it doesn't hurt. Where it does matter is that it also effectively "resets" your rule, unscheduling any waits, delays, and other timed actions or actions that create temporary subscriptions (so basically, you'll need another trigger event to start your rule actions over again--keep this in mind if, say, you're using Private Boolean and setting it false at the end of your rule after a wait or delay).