It was only mentioned in passing at the Google I/O developers conference, but Google announced the ability for smartphones running Android M with USB Type-C (Apple simply calls it USB-C) ports to recharge other smartphones. The potential here is enormous.
Your phone's battery can be used like an external battery pack for other devices. With a two-way USB Type-C cable, you could quickly "lend" a friend's dying smartphone some quick power. Smartwatches could also adopt USB Type-C ports instead of using proprietary wireless charging docks Smartwatches could also adopt USB Type-C ports instead of using proprietary wireless charging docks and be recharged from your smartphone when they're running low on power.
Obviously, it wouldn't make much sense to use your phone to charge a tablet or laptop.
Whether or not you embrace it, USB Type-C is the future of connectivity. Not only is it reversible, but it's also very versatile: It can provide power, output video and transfer data. On laptops, it's a little more controversial; accessories still haven't adopted USB Type-C (yet) and you'll need to buy dongles or external docks to regain all your legacy ports.
On a smartphone or tablet, though, USB Type-C is perfect. In the future, you may not have to carry around an external battery brick or case, or find an outlet. Instead, you'll be able to ask a friend for a quick recharge. That person, however, will have to be okay with draining their own phone to juice up yours, though.
That's what friends are for, right?