So I have just begun to start wanting to spend my Ecency points but was initially a little confused.
I seen the option to "boost" and the option to "promote" and at first I wasn't sure what the difference was, but after some quick research on the Ecency Community Page I found my answer.
"Boosting" your post is essentially getting an Upvote from Ecency, but first it is reviewed. If your account is blacklisted or the posts don't meet Ecency's criteria, then you will be denied the boost and your Ecency points will be returned to you within 24 hours.
In short, not all posts get boosted so make sure to blog quality!
And the second option to "Promote" does just that; promote. It simply puts your post back in the feed via promotion. If you ever scroll on Ecency you will notice promoted post and this is how that's done!
All posts will get promoted as long as you have to points to afford it!
Anyhow hope this helps with anyone confused about Ecency points like I was!