Well first of all it requires the Twink-BG Exploit ([Twink glitch] Great news, enter leveling bg with xp-off is back!).
Form a group with your twinking friends, just say for example youre 5 twinks in this grp.
You unlock your exp, join the normal que as usual and then do the exploit to get in the normal BGs.
You will get a Deserteur-Debuff from that, but youre still in the BG.
If you write /afk now, you WONT get kicked out of the BG nor the BG Group, BUT an other NEW player will be invited. You get your deserteur refreshed to 15min again but its 15min at the start of the BG anyway.
So if 5 twinks made it in a normal BG, they can easily just /afk and then play a WSG with 15vs10 for superior GY-farming for example.
When you /afked while Deserteur-debuff you wont be showed as flag carrier while holding the flag and you wont be showed on the scoreboard anymore. On the scoreboard its still 10vs10 even if there are 15 players in your team.
Well, i know that this exploit does not have that much potential cause it cant be used on 90, but lets say you still need Arathis-Basin-Perfection. Just join with 5 twink friends and play it 20vs15, easy win.
My english is not perfect but i think everybody should understand this.