Facebook has always limited the exposure of posts by brands (and to some degree individuals) based on the EdgeRank system and aside from very small pages, the rates tend to be pretty low as let's face it, over time people just get less interested in what you have to say.
Thus we get to Promoted Posts which let you up the exposure level. This isn't something you need to use on every post, in fact I'd say the effects will be fairly counter to do that (there's a reason why your exposure drops) but for the right announcement, question or share it's very compelling.
You can find the feature in the options under the new post box (click to activate). As is the usual for a Facebook rollout not all pages have the feature yet but you can see how it looks @ http://marketingland.com/facebooks-promoted-posts-rolling-out-heres-what-it-looks-like-12917
Of course if there's a move to hard cap visibility away from engagement / relevancy that would be a big change. Don't suppose you remember where you saw that info?