I also did not know that there are different qualities of fog... I thought fog is fog, but it seems that some fog machines are really better than others. One of the aspects of fog quality is being able to breathe even when there's lot of it. One one occasion, we fogged a studio so much that I could not see my own hand 6inches from my eyes, and I was still breathing normally as if the air war pure. I couldn't say if it has long-terms effects if you breathe too much of it though, but I can say that not coughing with so much fog is quite impressive.
Also, don't get caught speaking of "smoke" to these people, who take a lot of pride in their product :) It's fog and haze... not smoke!
Everything lighting in the show we had preprogrammed before the show season. The only decisions I made during each night's show were when to go to the next look. Except for the fog - I ran the fog machines manualy from faders on my control board. It was one of my favorite parts of the show because required on the spot, improvisational artistry.