For a nonprofit entity that I am affiliated with, we had a very high engagement (free) Facebook presence that eroded over time as organic posts get crowded out.

So you end up boosting or wasting money on ads. In my (limited) experience, ads weren't effective for us as they were too local and the audience was limited. Boosts were effective but expensive.

The funny thing was the our highest conversion paid event advertising was the old fashioned newspaper.