With this glitch, you can loot the first boss in LFR as many times as you want! I know some people need like 4 items or so from that boss, so that would be very useful for them. I am not sure if you can get more legendary pieces since I don't have the quest on this character.
The video shows exactly what to do, and what you'd expect as results. Read the instructions and see the video before asking questions and telling me that it doesn't work. If it doesn't work, you're doing something wrong.
Instructions:
1. Join "Walled City" in Looking for Raid.
2. Reach the arena part where Kargath spawns.
3. Do nothing. Don't attack, just target yourself or something and be semi-afk. Don't even attack the trash. Don't die, not sure what happens if you do.
4. When the rest of the group has killed the boss, leave and you'll receive your drops in mailbox without being locked. DO NOT LOOT KARGATH! Extra rolls are fine to use, and has been tested.
Voíla!
Be cautious. Players have been suspended for similar exploits before, and just as any other exploit on this forum, use it at your own risk.
Edit 1: Disenchanting the gear may yield a good profit on some servers.
Edit 2: Even if you're locked, it seems you can still do it again. Same thing applies, don't attack.
Edit 3: Just wanna point out that you do not need to finish, you can just leave after Kargath.
Edit 4: Long queue time? Ask a healer to queue you in for 100g or so. It's worth it.
Edit 5: Receiving a lot of runes? That means it's working, keep going.
Edit 6: Some have claimed this is working on Tectus aswell. Can we confirm this?