Imagine a jar full of marbles. Imagine there’s a shit ton of random large gaps between some marbles across the jar. You can remove those gaps and redistribute the marbles more evenly by smacking the jar. You then end up with bigger groups of closer marbles.

Folding is smacking the jar. It redistributes the atoms in the material in a more homogeneous, more consistent, more uniform way. That’s desirable in materials that are made up of lattices, e.g. steel. Makes them stronger overall because now you have larger groups of atoms connected to each other, fewer gaps within the material.