Coffee beans alone don't make a drink, but take two, and the cup fills. In the quantum world, there are similar states: from one copy, you can't extract pure entanglement, but from several, sometimes you can. For a long time, it wasn't known if such a thing existed at all.
Scientists took a family of states specifically designed as a testing ground for this question. One state in the family turned out to be a surprise: one copy (nothing, two copies) there's a result. And this holds for any system size, starting from three.
Next to this state, they found a whole region where two copies already work. A bit further, there's another region where even two copies don't help. Between them lies a band where it's still unknown how many copies will be needed.
Thus, one family of states showed that the boundary between 'hopeless' and 'useful' quantum resources is not a straight line. It bends, and within it there are islands where the second copy makes all the difference.
Entanglement cannot be copied: if you have one entangled pair of particles, you cannot make a second identical one without destroying the first. So the question 'how many copies are needed for purification' is not idle: it's about how to manage a limited resource.