Astro healing: What to expect?

[Miiu]

All you can do ist trust your healer(no matter the class). But an AST should never wait for the tank or player to drop to dangerous levels just to get the maximum out of ED.
On a personal note depends (on the encounter though) but most of the time ED is used after "unexpected" dmg or hard hitting abilties and the tank dropped to an hp amount I am not comfortable with waiting for benefic II. I pretty much use it like lustrates on SCH except that I can only use it once every 40 seconds.

*edit*

In the end even though I always joke in dungeons when tanks pop "HG / Holm / LD" and "complain" about them having no trust at all, still follow your own instinct. If you think you need to pop Holmgang, use it. Unless its inside raid content where you actually want to save those cooldowns for certain mechanics etc.