when owning two dogs its one thing, but something about going from 2 to three you now have a pack mentality and things change quite a bit. Most people are not familiar with dog behavior enough to know when to interrupt something that can go wrong.
Without having that knowledge you have to rely heavily on the dogs actually getting a long. This is not always the case, and just like humans, some dogs just DON'T get a long.
So I think it entirely depends on the person. I manage my 8 dogs quite well and board my clients dogs regularly. I often get comments on how amazed people are at how well behaved my dogs are and how easy they are to manage. When using obedience, and then interrupting behaviors that can lead to problems, it makes handling them that much easier.
In another home, this entire pack structure may not work.
"For the animal shall not be measured by man. In a world older and more complete than ours they move finished and complete, gifted with extensions of the senses we have lost or never attained, living by voices we shall never hear."