Parag Khanna emphazises their importance:
[P]recisely how will this collection of nations influence the course of world events? It is important to note that not all of these emerging states are on a linear path toward regional-power status. Some will rise while others stumble. But collectively, the ones that rise will exercise a significant pull on events. One reason I repurposed the term Second World for these countries was to emphasize their internally divided nature, embodying both First World and Third World attributes. Of the approximately two hundred states in the world today, only thirty are members of the First World club of the Organisation for Economic Co-operation and Development (OECD). Meanwhile, the bottom forty-eight (mostly in Africa) are formally labeled Least Developed Countries (LDCs). In between lie the Second World nations.
There are about a hundred of them, and there is little certainty these days over which ones will rise into the First World and which will descend into the bottom category.