Implement hook_order_state() hook

What exactly is that hook for and why this module should implement it?

IIRC, that hook just defines states and statuses (or just states?). In any case I don't see any need for this module to define additional states or status. The already defined one (payment received, completed, etc.) should be enough. At least they were so far.

I don't see the need of implementing this, if needed, please re-open and provide more information.