We all know about Smoke Flares, right? You can use them in BGs! When you place around 20 in the same spot, it can create some major lag for those running over it. I have a great gaming computer and I still experience lag running through it.
Like in the pic above, you can put them in the compact spaces in WSG where the opposing faction must run through, like the tunnel or ramp. It will work better if you make 3 or 4 groups of them rather than just one.
It is very easy to place them, too. Just bind it to a key and press it then click. Don't move your mouse and place another one on the same spot. With a cooldown of only about 3-4 seconds, you could put a lot of them on the same spot before they start to despawn.