They are really two completely different devices (5v direct PTs vs 3.7v inline battery PTs).
People use USB ports for all sorts of things. And those "things" can all malfunction. Coffee warmers, fans, gizmos. The cautions above are prudent... use a wall wart.
If you're using a 3.7 volt PT with a battery... just get a wall wart on your next order of hardware/juice so you don't have to pay extra shipping. You don't have to run out today and buy a wall wart in a panic. It frees up a port too, and lets you vape without your computer... like by the sofa.
If you're using a 5v PT... no battery. Even for USB 3.0, get a wall wart!