Boosting a post is most often an engagement ad, although recent updates have given users the ability to adjust the type or campaign to traffic if you want.
I admit that I use the boost button specifically to get my posts to be seen by my own audiences. I have saved audiences that I boost too. It keeps people reminded of my business, services and value I provide.
This is part of a larger strategy where i run offer ads and lead generation, to cold audiences and people who’ve interacted with my page but are not on my email list.
In general using the Ad Manager is the best way to run high quality advertising from Facebook. You have many more options as far as types of campaigns, audiences and creative.
Boosting a post is just a “gateway” into running better ads. In all honesty my first Facebook ad was a boost for $1, now I run campaigns spending thousands of dollars a day for clients. (not boosting)
You are better to take a look at the Facebook Blueprint course which is free training from Facebook. It will get you set up to run real campaigns based on your desired outcomes.
With Ad Manager and the Facebook Pixel you can track actual ROI per adset and down to the ad level. This lets you optimize and spend more where it is getting you the best return.
Just boosting doesn’t give you the insights that the Ad Manager does.