Depends on the room really. Some rooms, the air moves a certain way and if you don't place the hazer in the right spot, you will end up with just clouds in certain airs. Smaller rooms, this generally isn't an issue however.
It also depends on how big a hazer you are using to how large of a space you are trying to fill. I have had no issues with my HZ-500 filling out a room but an X310 is no where near as even. So if you are using a lower output hazer, you might need to experiment with different positions a bit more.