Many of us will have read posts about the tactics for Shunting, and the vast majority of them will be about the late game shunt to deny the enemy objectives. This is a valid tactic, and I am sure it works very well for the people talking about it.
However for me, I have found this tactic doesnt work so well. Grey Knights are an expensive force, and my main opponent is Tom, his Space Wolves are having great fun annhilating my Grey Knights at the moment (helped by a solid list, my poor tactics and what I feel may be weighted dice for his AP2&1 Weaponary).
Now the Tactic I have found that works well (against all but him) is used when I have two Dreadknights with personnal Teleporters and a unit of Interceptors (10 man).
This allows me to Shunt 3 units straight at his battle lines early in the game. He then has to spend time dealing with these units before advancing onto the rest of my army. This is a tactic that my army list relies on, and to be fair it needs perhaps another Dreadknight or Interceptor squad to make it work effectively against him.
By forcing your enemy to deal with your units at the very beginning of the game they are having to change their plan of action on how they intend to get to the rest of your forces. To me the Grey Knights are an aggressive force at all points levels. I want my army to get in your face and to force you to make decisions quickly.
It doesnt always work, and against an army with plenty of AP3 or better you want to be carefull of where you arrive.
The shooting you do after the shunt is also very important, you need to stop or reduce the threats close to you, and with good positioning you want to bring the enemy closer to your shunters, where you can bring more firepower to bear on them.
Admittedly I build my army lists around this tactic, and it has worked very well at the last two tournaments I went to. No one expected it, and no one was able to deal with two Dreadknights in their face so quickly in the 1000 point games, and no one was able to deal with the two Dreadknights & 10 Interceptors in the 1750 point games.
In fact the only person I know that has effectively dealt with the army is my good friend and constant advesary Tom. His Space Wolf list has the right balance of AP2 & AP3 weaponary to deal with both the Dreads and Interceptors.
In the end though the tactic can be a bit of a one trick pony, but in a tournament, that can certainly be all you need!