Mats and skin can become indistinguishable to the untrained person, you pull up what you think it a mat, and you cut skin....bad. Its very easy to do if you do not know exactly what you are doing.

As far as the "blue comb" (thats what we called them, dont know why, they arent blue!) (snap on combs), You dont eyeball it, you brush the dog out before you use it. And trust me, if you hit even the slightest tangle, it stops. Those are actually good tools for the amateur as you will figure out quickly when your dog is mat-free or not, and they are pretty hard to injure a dog with, though they are also easy to leave an uneven trim especially on legs.

CN