Let me explain what you really need to know, so you don’t accidentally harm yourself or use “tricks” that burn out.
See below for how I spent $976, but set a budget of only $290 on a boosted post.
You can promote a post from Ads Manager or Power Editor, and also boost the post right there from Insights or the timeline. 90% of the time, I’m lazy and will boost right there, since I can easily see organic engagement, comments, and other bit that you don’t get in Ads Manager.
But if I want to add another audience to run alongside this boost, I can’t. With a boosted post, I can only change that single audience and budget– not have multiple ad sets.
So that’s why a STACKED boost is when you let the original boost run, but also promote that post in Ads Manager– so you have multiple audiences running at the same time.
The minor downside is that it looks as if you overspent the budget– not a bug. The $290 is for the boost, not the other ad sets in Ads Manager promoting that same post.
That’s why sometimes you might see a post that has an orange bar (meaning there is ad spend on it), but still have an option to boost. It’s already being promoted somewhere else, but just not boosted from the timeline.
Clear as mud?