That's not exactly how this works; you can just maintain simultaneous connections over both network methods. This consumes a very small amount of data on both, but will intelligently shift the bulk of data between the two as connectivity/packet loss/etc changes. It's about being able to seamlessly go from one to the other and back again without having to halt and re-open TCP connections every time, not about using both connections full-out all the time.

Checkout the tech talk if you want to know more.