What is hierarchy to collections ? 

Hierarchy to collections is an addon which allows you to have both empty hierarchy (from Maya or 3Ds Max import) and a collections hierarchy in the same file.

From Maya, Blender 2.79 or 3dsMax to Blender 2.80+

If you import a model from Maya for exemple, it will gives you an empty hierarchy. With this addon, you can convert it in a collection hierarchy easily !

From Blender 2.8+ to another software

You have also the opportunity to convert collection hierarchy to an empty hierarchy, in order to share your model with other softwares