John, a lot of people mow without the guards, and may never have a problem, but as with taking risks in any activity, there also may be serious consequences. The first time I mowed my pasture I had no guards on my brush hog; just light weeds and grass to mow, although some of it was under some pecan trees. There was a little dead limb in the grass that I didn't see and when that little 4' brush hog shot a piece about the size of my arm out in front of me about 50', I decided I needed the guards. Imagine the force it would take to throw something low enough to go under a little tractor and yet stay in the air 50'. I think it if had hit a tire, hydraulic line, etc. under the tractor, there definitely would have been some damage. I've not personally known of anyone injured by flying debris from a brush hog (although I've heard of it happening), but I've personally known of damage to buildings from it. There's a considerable possibility of damage to anything or anyone within 100', or more, of a mower without guards.
The best guards, in my opinion, are chain guards. They can be a bit expensive, but I made my own for two brush hogs. Next best is probably those made from something like conveyor belt material (rubber and fiber).
