A lot of the "sit" exploits hurt you more than help you. For example:
The combustion one, when your sitting, you will not proc ignites on the target, your set bonuses and trinkets will not proc, you will not get mana return from master of elements, or the threat reduction from Burning Soul. Tie all that into having to be sitting while the spell lands, and its pretty useless unless you can stack like 1500 spell damage.
This was taken from radikalnoise.com