In the past, lights using rechargeable batteries required specialized and often bulky chargers and cables. USB Charge capability allows you to use standard Micro USB cables to plug into the light directly or even directly into the battery to quickly top off your charge with home and car cables/charges that you already have on hand.
Rechargeable batteries save money and are capable of higher light output, but are susceptible to power drain while not in use and are not always practical for use in the field. Dual Fuel is a design concept that allows lights to run off of rechargeable or standard disposable batteries, increasing the capability of your lights and giving you the best of both worlds.
This capability allows you to use your Browning light to keep your USB electronic devices charged. Your smartphone might be your only link to first responders in the event of an emergency. It could also be serving as your primary map/navigation device, camera, etc. Keep your phone and a host of other devices charged when you need them most.