To me a knife is a tool, to be used and enjoyed in the good times and must be designed to meet the worst times. The greater the margin of safety the maker can develop in his knives and scabbards the better for the man who pays his bills, his client.
There seems to be a macho image for some to use a knife without a guard, to me it is a needless risk. When I worked on a kill floor I could leg, skin, face head and gut a cow as fast as any and my knife had a full guard.
Years ago one of my students decided he did not want a guard on his knife, he was handy enough (macho) it was not necessary for him. He was hired on as a guide and camp cook for an elk hunt. He was skinning an elk, his hand slipped onto his pride and joy knife without a guard and the entire party (12) hunters, had to cut their pack trip short, break camp and to take him 15 miles back to the highway, then to the hospital. Six hours of surgery, 3 months rehab and years later he can use his hand pretty good, about 40 % recovery, except for his trigger and middle fingers. A cut tendon is a serious event and can take years to heal. I choose not to take the risk.
This summer a student to one of our seminars handed me a knife with out a guard, the handle design was like a slide onto the blade. Just holding it sent a chill down my back. Personally I would not use that knife to sharpen a pencil.
A three piece knife is time saver to make. To develop a guard with a high degree of functional qualities takes me about 6 hours, but for me it is worth it.
There are significant differences in knives and there are many choices. This is a good thing, freedom to make what you believe in and freedom to chose what you will carry.
We all make our choices and then have to live with them.