The concept of "rooting" an Android device means to unlock a part of the file system that is kept read / write by default. There are many reasons for this, such as it means a clumsy user cannot inadvertently delete a critical part of the device and stop it from working properly. It also means that malicious applications cannot interfere with the device such as inserting malware into core components: some applications designed to be secure, such as mobile banking applications, check to see if a device has been rooted and if it has, they refuse to run. However, the advantages of gaining full access to all of your device include the ability to remove bloat applications that you do not need, such as those your carrier kindly bundled in with the device, or perhaps change advanced parameters in the device that Android or your device manufacturer doesn't support as standard. Different devices are more or less difficult to root, depending on a number of factors.
The LG G4 is one of the most talked about flagship Android handsets this year, thanks to LG's interesting component decisions. The G4 is based around the Qualcomm Snapdragon 808 chipset, one notch down from the early 2015 flagship chip. Instead, LG have provided the G4 with an industry-leading camera and a superb bright, sharp and colorful display. When it comes to gaining root access, in the case of the unlocked devices straight from LG, these have been opened up for some time but for those G4s purchased via the carrier, it wasn't possible to root these devices just yet. Now, thanks to XDA Developers forum member, thecubed, and a number of other individuals who helped him, the carrier-branded models may be rooted using the new "Low Effort Root" technique. However, there are some caveats here and the first is that the process is potentially dangerous: there are several steps and each one must be perfectly followed as a wrong step could result in a bricked device. The method of rooting relies on reflashing a pre-rooted system image to the device (and this explains the risk of destroying your G4). G4 customers will need the correct drivers installed on their computer and to download the correct firmware, which you can find on the XDA Forums source below together with detailed instructions.
As a caveat, if you are reading this article with a LG G4 bought from one of the North American carriers and are wondering why you might want to root your device, the golden rule here is that if you know a reason, go right ahead. However, given the danger that installing the new software image onto the wrong partition will destroy the device, this is not something I could possibly recommend doing to a loved one, or a work device, just in case to turn that expensive G4 into an expensive model of something that used to be the G4!