For me, the bottom line is that you should use ED as it is intended - for situations where you have an absolute clear favorite choice, that you are sure is going to be both affordable and a good fit, and that you are already sitting with a decent chance of admission (i.e., sitting above the midpoint of the freshman class stats in terms of scores/GPA/course load/etc.) Trying to strategize with ED is largely a fool’s errand - if a school is a big long shot for you RD, ED will very likely end result in nothing more than an early rejection letter.
There are some particular exceptions to this rule of course (what good rule doesn’t have them?) - if you are solid candidate for HYPMS, and you are dead set on an Ivy, then you should take advantage of SCEA (I know, not ED technically.) If you are a Penn legacy with a decent shot at admission, you need to do ED. And I am sure there are others I don’t know about. Most of the time however, I would stick with the paragraph above as guidance.