I used promoted post/Boost post and experienced some Good and bad sides of this feature.
1. Easy to launch. No technical knowledge. Just few clicks.
2. Budget friendly.
1. It will reach to the peoples who have liked the page and their friends only.
2. You have to pay more to reach to more people.
3. Its not easy to create engagement by promoted post.
4. Its just a waste of money if you want to increase your likes/Fans.
Promoted post is better for small business to promote their offer and events. For increasing likes and spreading through a specific class people Advertising better than promoted post.
So, Above all, Facebook Promoted Post Sucks.