My S applied ED to his school because it was a very clear favorite, he was applying to a competitive program even though the school in general is not terribly competitive for admission, and the school listed the qualifications needed for specific merit amounts on the website. So we knew exactly how much merit he would get.
Oldest did a couple of EA schools because they had EA and it would have been nice to know earlier (she was deferred at both, accepted to one later on but did not go there). Also one required EA for merit scholarship consideration.
Youngest did not apply ED anywhere because she had no clear favorite, but she did apply widely to competitive schools and had great results.