There was a program that I was considering applying ED to. This school had an articulation agreement with my college as well as a few others. This agreement gave preferential admission to students from these agreement schools who had a gpa of 3.25 or higher in certain prereqs.
When I met with them they told me that I was as good as in if I applied ED. However, there are only ~40 spots per class and they fill up about 30-35 of those seats with ED and internal applicants. They told me the only people who would get those las 5-10 seats or so were the top of the top. If you wanted to get in as a more average student, you needed to go ED.
I'm not sure if this is representative of other programs but I hope this helps a little!
Oh, and yeah: I decided to not apply ED to this program. I'm just going to apply regular decision to them and 9 other places.