I work alone. Very seldom is there someone around. I think its more good than bad. Less people to get hurt with the tractor or saw. I have worked with the saw around other people and I don't like it. I would have to watch ME, the saw, the tree AND someone else. I had to yell at them a few times to get back.
For the fatal saw accidents I have read about, having someone else present would have just been a witness. Not a thing they could have done to prevent the person from dying. The people could have been outside a trauma room and they would have bled out before they got inside.
Surely there is an injury where a witness could prevent death but it seems like most of the accidents are either immediately fatal or you have time to get to the ER. In any case I don't have much choice. If I had to have someone watch me work no work would get done.
My rules are to be aware, not tired, wear the safety equipment, tools have to be in working order, THINK, and go slow. Violate any of the above and stop work.
Later,
Dan