The LG G6 supports Quick Charge 3.0 fast battery-charging technology. So what is it useful? because unlike the LG G5, the G6 doesn't have a removable battery. You won't be carrying a second battery to replace the one in the phone once the battery dies. Your only option will be to charge your phone. The problem with charging your phone is that it takes a long time. This is why many people charge their phone when they get home from work and leave it to charge fully through the night.
With Quick Charge 3.0, you can charge your phone much faster. LG didn't provide any exact figures, and of course the charging time depends on the battery capacity. In the official Qualcomm's Quick Charge, a 5 minutes charge can give you 5 hours of battery life. Even if those aren't the exact numbers, you get the point. Spend less time tethered to an outlet and more time using your phone freely without any cables.
Some of the other QC3.0 supported phones are HTC 10, HTC U Ultra, HO Elite x3, LG G5, LG V20, Asus ZenFone 3 Deluxe and many other, all those phone use either Snapdragon 821 or 820 processor which come with support for this technology. There is also the HTC One A9 that uses the SD617 that also supports QC3.0, at least that what Qualcomm's website shows.
Being able to quickly charge your phone is a god send feature. Anyone can benefit from it, especially when spending a lot of time outdoors and taking advantage of the many multimedia features that the LG G6 has to offer, like watching movies, playing games, or using the camera for capturing images and videos. These all things consume a lot of power, even the screen itself because of its high resolution consumes a lot of power. I've already read on some website that the LG G6 battery is about average, nothing spectacular. It's also a 3300 mAh battery, so I didn't expect it to be anything out of the ordinary.
So if the battery drains quickly for you, you can always stop by a restaurant and charge the phone for a few minutes to get more charge and continue doing whatever you had been doing. I personally would have loved to have a replaceable battery and just carry a second full battery with me without using all these advanced technologies. However, the LG G6 comes with a unibody design with a glass back that is not going anywhere. If you want more power, you'll need to charge your phone. At least if that happens, you know that you can do it really fast without waiting an hour to get a decent charge to continue using your phone.
Quick Charge 3.0 support according to the features as seen here on lge.co.kr.