If you root, you're on your own. Prior to rooting, make sure you do standard tests on the phone (battery, phone call, text, browsing, multitasking, running stock apps including camera, etc.). Once you root, if you have any software issues, you can most likely resolve this by flashing the phone (next step up from factory reset). An improper flash may back-fire, but you can flash the phone as many times as you like.
Next factor your cost of replacement. A 1 yr warranty is a bit weak given that it's a 2 yr subsidy agreement. Say you root and void that 1 yr warranty, your buy-out may be a bit high. If you're on a budget phone, it's a no brainer. Root away, they're so cheap on promo to replace. LG G4 is priced as a mid-range, cost of replacement is a bit higher.
Still, any software issue can probably be resolved by flashing. I've bricked phones several times, flashed them, then back in business. Personally, I'd root a G4. I've never relied on manufacturer warranty for phones, either. I've had some fuctionality issues with older phones (which were common issues reported by many users of the same handsets) and found that the best option was to change handsets. My Moto X Play is rooted, and it was a mid-range. Got it May last year, meaning if it were still under warranty, I'd still have a few months. Phone's been working great and got *most* of the tweaks I wanted via rooting.
There is no real reason to root nowadays, in my opinion. This coming from someone who used to root just about every Android device I could get my hands on, since the days of Gingerbread. Manufacturers warn that OTA updates will not be delivered to your device. This means that if you want to receive the latest security or system updates, you'll have to un-root and re-lock the bootloader. Best to just wait for Android N, if in fact it's headed for the G4.
I used root to perform NANDroid backups, (full system backups). Something that hasn't been mentioned here and should be one of the first things performed after installing a custom recovery. Moving system and user apps to an SD card and overclocking the CPU were other reasons for gaining root access. Somewhat redundant, now that we have phones with quad, hexa-core and octa-core processors with plenty of RAM.